ECMAScript® 2024 语言规范
关于本规范
在 https://tc39.es/ecma262/ 上的文档是最准确和最新的ECMAScript规范。它包含了最新年度快照的内容以及任何已完成的提案（那些在提案流程中达到第4阶段并因此在多个实现中实现且将在下一次实际修订中包含的提案）自该快照以来的内容。
为此规范做贡献
此规范在GitHub上由ECMAScript社区的帮助下开发。有多种方式可以为此规范的发展做出贡献：
- GitHub Repository: https://github.com/tc39/ecma262
- Issues: All Issues, File a New Issue
- Pull Requests: All Pull Requests, Create a New Pull Request
- Test Suite: Test262
- 编辑:
-
社区:
- Discourse: https://es.discourse.group
- Chat: Matrix
- Mailing
List Archives: https://esdiscuss.org/
有关如何创建此文档的更多信息，请参阅
导言
此ecma标准定义了ECMAScript 2024语言。它是ECMAScript语言的第十五版 规范。自1997年第一版出版以来，ECMAScript已发展成为世界上 最广泛使用的通用编程语言。它最为人所知的是嵌入在网络中的语言 浏览器，但也被广泛用于服务器和嵌入式应用程序。
ECMAScript基于几种原始技术，最著名的是JavaScript（Netscape）和 JScript（微软）。该语言由Netscape的Brendan Eich发明，首次出现在该公司的 Navigator 2.0浏览器。它已出现在Netscape的所有后续浏览器和Netscape的所有浏览器中 Microsoft从Internet Explorer 3.0开始。
ECMAScript语言规范的开发始于1996年11月。这个的第一版 ECMA标准于1997年6月由ECMA大会通过。
该ECMA标准已提交给ISO/IEC JTC 1以供快速通道程序采用，并被批准为 国际标准ISO/IEC 16262,1998年4月。ECMA大会于1998年6月批准了第二个 ECMA-262版本，使其完全符合ISO/IEC 16262。第一个和第二个之间的变化 版本本质上是编辑性的。
标准第三版引入了强大的正则表达式、更好的字符串处理、新的控件 语句、try/catch异常处理、更严格的错误定义、数字输出的格式和次要 对未来语言增长的预期变化。ECMAScript标准的第三版被 1999年12月的ECMA大会，并于2002年6月作为ISO/IEC 16262:2002发布。
第三版发布后，ECMAScript与全球广泛采用 Web，它已成为基本上所有Web浏览器都支持的编程语言。重要的 开发ECMAScript第四版的工作已经完成。然而，这项工作没有完成，也没有出版 作为ECMAScript的第四版，但其中一些被纳入了第六版的开发。
ECMAScript第五版（作为ECMA-262 5th版发布）事实上已编纂
对浏览器实现中常见的语言规范的解释并添加了
支持自第三版出版以来出现的新功能。这些功能包括
第五版提交给ISO/IEC JTC 1采用快速通道程序，并被批准为国际标准ISO/IEC 16262:2011。ECMAScript标准的5.1版包含了一些小的修正，文本与ISO/IEC 16262:2011相同。5.1版于2011年6月被Ecma大会采纳。
第六版的集中开发始于2009年，当时第五版正在准备出版。然而，在此之前，自1999年第三版发布以来，已经进行了大量的实验和语言增强设计工作。从某种意义上说，第六版的完成是十五年努力的结晶。本版的目标包括提供对大型应用程序、库创建的更好支持，并将ECMAScript用作其他语言的编译目标。其主要增强功能包括模块、类声明、词法块作用域、迭代器和生成器、用于异步编程的Promises、解构模式和正确的尾调用。ECMAScript内置库扩展了对附加数据抽象的支持，包括地图、集合和二进制数值数组，并在字符串和正则表达式中增加了对Unicode补充字符的支持。内置库还通过子类化变得可扩展。第六版为常规的、增量的语言和库增强提供了基础。第六版于2015年6月被大会采纳。
ECMAScript 2016是Ecma TC39在新的年度发布节奏和开放开发流程下发布的第一个ECMAScript版本。从ECMAScript
2015源文档生成了一个纯文本源文档，作为在GitHub上进一步开发的基础。在这一标准的开发过程中，提交了数百个拉取请求和问题，代表了成千上万个错误修复、编辑修正和其他改进。此外，还开发了许多软件工具来帮助这一工作，包括Ecmarkup、Ecmarkdown和Grammarkdown。ES2016还包括对新幂运算符的支持，并在Array.prototype中添加了一个名为includes的新方法。
ECMAScript 2017引入了异步函数、共享内存和原子操作，以及一些较小的语言和库增强、错误修复和编辑更新。异步函数通过提供Promise返回函数的语法来改进异步编程体验。共享内存和原子操作引入了一种新的内存模型，允许多代理程序使用原子操作进行通信，即使在并行CPU上也能确保定义明确的执行顺序。它还包括Object上的新静态方法：Object.values、Object.entries和Object.getOwnPropertyDescriptors。
ECMAScript
2018通过AsyncIterator协议和异步生成器引入了对异步迭代的支持。它还包括四个新的正则表达式特性：dotAll标志、命名捕获组、Unicode属性转义和后行断言。最后，它还包括对象的剩余和扩展属性。
ECMAScript
2019引入了一些新的内置函数：Array.prototype上的flat和flatMap用于扁平化数组，Object.fromEntries用于直接将Object.entries的返回值转化为新对象，以及String.prototype上的trimStart和trimEnd作为更好命名的替代方案，取代广泛实现但非标准的String.prototype.trimLeft和trimRight内置函数。此外，它还包括一些语法和语义的较小更新。更新的语法包括可选的catch绑定参数，并允许在字符串字面量中使用U+2028（行分隔符）和U+2029（段落分隔符）以与JSON保持一致。其他更新包括要求Array.prototype.sort为稳定排序，要求JSON.stringify无论输入如何都返回格式良好的UTF-8，以及通过要求Function.prototype.toString返回相应的原始源文本或标准占位符来进行明确。
ECMAScript
2020，第11版，引入了字符串的matchAll方法，用于生成全局正则表达式匹配对象的迭代器；import()语法，用于动态异步导入模块；BigInt，一种新的数字原始类型，用于处理任意精度的整数；Promise.allSettled，一种新的Promise组合器，不会短路；globalThis，一种通用的全局this值访问方式；专用的export * as ns from 'module'语法，用于模块内；增加了for-in枚举顺序的标准化；import.meta，一个由宿主填充的对象，包含关于模块的上下文信息；以及为处理“nullish”值（
ECMAScript
2021，第12版，引入了字符串的replaceAll方法；Promise.any，一个在输入值被实现时短路的Promise组合器；AggregateError，一种新错误类型，用于同时表示多个错误；逻辑赋值操作符（??=、&&=、||=）；WeakRef，用于引用目标对象而不保留其免于垃圾回收，以及FinalizationRegistry，用于管理在目标对象被垃圾回收时执行的清理操作的注册和取消注册；数字字面量的分隔符（1_000）；并且使Array.prototype.sort更加精确，减少了导致
ECMAScript 2022，第13版，引入了顶层await，允许在模块顶层使用关键字；新的类元素：公共和私有实例字段、公共和私有静态字段、私有实例方法和访问器、以及私有静态方法和访问器；类中的静态块，用于每类评估初始化；#x in obj语法，用于测试对象上私有字段的存在；通过/d标志的正则表达式匹配索引，提供匹配子字符串的起始和结束索引；Error对象上的cause属性，用于记录错误中的因果链；用于字符串、数组和类型化数组的at方法，允许相对索引；以及Object.hasOwn，Object.prototype.hasOwnProperty的便捷替代。
ECMAScript
2023，第14版，引入了Array.prototype和TypedArray.prototype上的toSorted、toReversed、with、findLast和findLastIndex方法，以及Array.prototype上的toSpliced方法；增加了对文件开头#!注释的支持，以更好地促进可执行ECMAScript文件；并允许在弱集合中使用大多数符号作为键。
ECMAScript
2024，第15版，增加了调整和转移ArrayBuffers和SharedArrayBuffers大小的功能；添加了用于创建具有更高级功能的字符串集的RegExp/v标志；引入了用于构建Promise的便捷方法Promise.withResolvers、用于数据聚合的Object.groupBy和Map.groupBy方法、用于异步等待共享内存更改的Atomics.waitAsync方法，以及用于检查和确保字符串仅包含格式良好的Unicode的String.prototype.isWellFormed和String.prototype.toWellFormed方法。
代表许多组织的数十个人在Ecma TC39中对这一版本的开发以及之前的版本做出了非常重要的贡献。此外，还出现了一个支持TC39的ECMAScript工作的活跃社区。这个社区审查了无数草案，提交了数千个错误报告，进行了实现实验，贡献了测试套件，并向全球开发者社区介绍了ECMAScript。不幸的是，不可能识别和感谢每一个为这项工作做出贡献的人和组织。
Allen Wirfs-Brock
ECMA-262，第六版项目编辑
Brian Terlson
ECMA-262，第七版至第十版项目编辑
Jordan Harband
ECMA-262，第十版至第十二版项目编辑
Shu-yu Guo
ECMA-262，第十二版至第十五版项目编辑
Michael Ficarra
ECMA-262，第十二版至第十五版项目编辑
Kevin Gibbons
ECMA-262，第十二版至第十五版项目编辑
1 范围
本标准定义了ECMAScript 2024通用编程语言。
2 一致性
符合ECMAScript规范的实现必须提供并支持本规范中描述的所有类型、值、对象、属性、函数和程序语法及语义。
符合ECMAScript规范的实现必须按照最新版本的Unicode标准和ISO/IEC 10646解释源文本输入。
提供支持不同语言和国家的语言和文化习俗的应用编程接口（API）的符合ECMAScript规范的实现必须实现ECMA-402最新版本中与本规范兼容的接口。
符合ECMAScript规范的实现可以提供本规范中未描述的其他类型、值、对象、属性和函数。特别是，符合ECMAScript规范的实现可以为本规范中描述的对象提供本规范中未描述的属性和值。
符合ECMAScript规范的实现可以支持本规范中未描述的程序和正则表达式语法。特别是，符合ECMAScript规范的实现可以支持使用本规范第
符合ECMAScript规范的实现不得实现本规范第
符合ECMAScript规范的实现不得重新定义任何不是
符合ECMAScript规范的实现可以选择实现或不实现规范性可选的小节。如果实现了任何规范性可选行为，则必须实现包含的规范性可选条款中的所有行为。本规范中用彩色框中的“规范性可选”一词来表示规范性可选条款，如下所示。
2.1 示例规范性可选条款标题
示例条款内容。
符合ECMAScript规范的实现必须实现遗留小节，除非它们也被标记为规范性可选。遗留小节中指定的所有语言特性和行为都具有一个或多个不理想的特性。然而，它们在现有应用程序中的持续使用阻止了它们从本规范中删除。这些特性不被视为ECMAScript核心语言的一部分。程序员在编写新的ECMAScript代码时不应使用或假设这些特性和行为的存在。
2.2 示例遗留条款标题
示例条款内容。
2.3 示例遗留规范性可选条款标题
示例条款内容。
3 规范性引用
下列引用文件对于本文档的应用是必不可少的。对于有日期的引用，仅适用于所引用的版本。对于无日期的引用，适用于引用文件的最新版本（包括任何修正案）。
Unicode 标准。
https://unicode.org/versions/latest
ISO/IEC 10646，信息技术 — 通用多八位编码字符集 (UCS) 加上修正案1:2005、修正案2:2006、修正案3:2008、修正案4:2008和其他修正案和勘误，或其后续版本。
ECMA-402，ECMAScript 国际化 API 规范，特别是与本规范版本相对应的年度版。
https://www.ecma-international.org/publications-and-standards/standards/ecma-402/
ECMA-404，JSON 数据交换格式。
https://www.ecma-international.org/publications-and-standards/standards/ecma-404/
4 概述
本节包含 ECMAScript 语言的非规范性概述。
ECMAScript 是一种面向对象的编程语言，用于在 宿主环境 中执行计算和操作计算对象。本规范中定义的 ECMAScript 并不打算是计算自给自足的；实际上，本规范没有规定外部数据的输入或计算结果的输出。相反，预计 ECMAScript 程序的计算环境不仅会提供本规范中描述的对象和其他设施，还会提供某些环境特定的对象，这些对象的描述和行为超出了本规范的范围，只是表明它们可能提供某些属性可以从 ECMAScript 程序中访问和调用的函数。
ECMAScript 最初设计为一种脚本语言，但现已广泛用作通用编程语言。脚本语言 是一种用于操作、定制和自动化现有系统功能的编程语言。在这些系统中，有用的功能已经通过用户界面可用，脚本语言是将这些功能暴露给程序控制的机制。这样，现有系统就提供了一个对象和设施的 宿主环境，从而完善了脚本语言的功能。脚本语言旨在供专业和非专业程序员使用。
ECMAScript 最初设计为一种 Web 脚本语言，提供一种机制来在浏览器中使网页生动起来，并作为基于 Web 的客户端-服务器架构的一部分执行服务器计算。ECMAScript 现在用于为各种 宿主环境 提供核心脚本功能。因此，本文件中规定的核心语言与任何特定的 宿主环境 无关。
ECMAScript 的使用已经超出了简单的脚本编写，它现在用于许多不同环境和规模的全方位编程任务。随着 ECMAScript 使用范围的扩大，它提供的功能和设施也在扩展。ECMAScript 现在是一种功能齐全的通用编程语言。
4.1 Web脚本
Web浏览器为客户端计算提供了一个ECMAScript 宿主环境，包括表示窗口、菜单、弹出窗口、对话框、文本区域、锚点、框架、历史记录、Cookies以及输入/输出的对象。此外，宿主环境还提供了一种将脚本代码附加到事件（如焦点更改、页面和图像加载、卸载、错误和中止、选择、表单提交和鼠标操作）的方法。脚本代码出现在HTML中，显示的页面是用户界面元素和固定和计算文本及图像的组合。脚本代码对用户交互有反应，因此不需要主程序。
Web服务器为服务器端计算提供了不同的宿主环境，包括表示请求、客户端和文件的对象；以及锁定和共享数据的机制。通过结合使用浏览器端和服务器端脚本，可以在客户端和服务器之间分配计算，同时为基于Web的应用程序提供定制的用户界面。
每个支持ECMAScript的Web浏览器和服务器都提供自己的宿主环境，从而完成ECMAScript的执行环境。
4.2 宿主和实现
为了帮助将ECMAScript集成到宿主环境中，本规范将某些功能的定义（例如，抽象操作）全部或部分地推迟到本规范之外的来源。在编辑上，本规范区分了以下几种推迟定义的方式。
实现是进一步定义附录D中列出的功能或那些标记为实现定义或实现近似的功能的外部来源。在非正式使用中，实现是指具体的人工制品，例如特定的网络浏览器。
实现定义的功能是指将其定义推迟到外部来源而没有进一步的限定。本规范对特定行为没有做出任何建议，符合规范的实现可以在本规范提出的约束范围内选择任何行为。
实现近似的功能是指将其定义推迟到外部来源，同时建议一种理想行为。虽然符合规范的实现可以在本规范提出的约束范围内选择任何行为，但鼓励它们尽量接近理想。一些数学操作，例如Math.exp，属于实现近似。
宿主是进一步定义附录D中列出的功能，但不进一步定义其他实现定义或实现近似功能的外部来源。在非正式使用中，宿主是指以相同方式通过附录D与本规范接口的所有实现集，例如所有网络浏览器的集合。宿主通常是一个外部规范，例如WHATWG HTML (https://html.spec.whatwg.org/)。换句话说，宿主定义的功能通常在外部规范中进一步定义。
宿主挂钩 是一个由外部来源全部或部分定义的抽象操作。所有 宿主挂钩 必须列在附录 D 中。宿主挂钩 必须至少符合以下要求：
宿主定义 的功能是将其定义推迟到外部来源而没有进一步的限定，并列在附录 D 中。不是 宿主 的实现也可以提供 宿主定义 的功能定义。
宿主环境 是所有 宿主定义 功能的特定定义选择。宿主环境 通常包括允许获取输入和提供输出的对象或函数，作为 宿主定义 属性的一部分的 全局对象。
本规范遵循始终使用最具体术语的编辑约定。例如，如果一个功能是 宿主定义 的，则不应称其为 实现定义。
宿主和实现可以通过本规范中定义的语言类型、规范类型、抽象操作、语法生成、内在对象和内在符号与本规范接口。
4.3 ECMAScript 概述
以下是 ECMAScript 的非规范性概述，并未描述该语言的所有部分。该概述不属于标准的正式部分。
ECMAScript 是基于对象的：基本语言和宿主功能由对象提供，ECMAScript
程序是一个相互通信的对象集合。在 ECMAScript 中，对象 是具有零个或多个 属性 的集合，每个属性都有确定如何使用该属性的 特性 ——
例如，当属性的可写特性（Writable attribute）设置为
ECMAScript 定义了一组 内置对象，完善了 ECMAScript 实体的定义。这些内置对象包括 全局对象；对语言的 运行时语义 基本的对象，包括
Object、Function、Boolean、Symbol 及各种 Error
对象；表示和操作数值的对象，包括 Math、Number 和 Date；处理文本的对象 String 和
RegExp；值的索引集合的对象，包括 Array 和九种不同类型的元素具有特定数值表示的 Typed Arrays；键控集合，包括 Map
和 Set 对象；支持结构化数据的对象，包括 JSON
对象、ArrayBuffer、SharedArrayBuffer 和 DataView；支持控制抽象的对象，包括生成器函数和
Promise 对象；以及反射对象，包括 Proxy 和 Reflect。
ECMAScript 还定义了一组内置 运算符。ECMAScript 运算符包括各种一元运算符、乘法运算符、加法运算符、位移运算符、关系运算符、相等运算符、二进制位运算符、二进制逻辑运算符、赋值运算符和逗号运算符。
大型 ECMAScript 程序由 模块 支持，允许程序划分为多个语句和声明的序列。每个模块明确标识其使用的需要由其他模块提供的声明，以及哪些声明可供其他模块使用。
ECMAScript 语法故意类似于 Java 语法。ECMAScript 语法被放宽，以使其作为一种易于使用的脚本语言。例如，变量不需要声明其类型，属性也没有关联类型，定义的函数也不需要在调用之前出现在文本上。
4.3.1 对象
尽管 ECMAScript 包含类定义的语法，但 ECMAScript 对象并非如 C++、Smalltalk 或 Java 中的类为基础。相反，对象可以通过多种方式创建，包括字面量表示法或 构造函数，这些构造函数创建对象，然后通过为其属性分配初始值来初始化全部或部分对象。每个 构造函数 都是一个具有名为
new Date(2009, 11)
创建一个新的 Date 对象。不使用 new 调用 构造函数
会产生不同的结果，这取决于 构造函数。例如，Date()
生成当前日期和时间的字符串表示，而不是对象。
每个由 构造函数 创建的对象都有一个隐式引用（称为对象的
原型），指向其 构造函数 的
在基于类的面向对象语言中，通常状态由实例承载，方法由类承载，并且继承仅限于结构和行为。而在 ECMAScript 中，状态和方法由对象承载，而结构、行为和状态都是继承的。
所有不直接包含其原型所包含的特定属性的对象共享该属性及其值。图 1 说明了这一点：
CF 是一个 构造函数（也是一个对象）。通过使用
new
表达式创建了五个对象：cf1、cf2、cf3、cf4 和
cf5。这些对象每个都包含名为
与大多数基于类的对象语言不同，可以通过分配值动态地向对象添加属性。也就是说，构造函数 不需要命名或分配所有或任何构造对象的属性。在上图中，可以通过向 CFp 中的属性分配新值，为 cf1、cf2、cf3、cf4 和 cf5 添加一个新的共享属性。
尽管 ECMAScript 对象本质上不是基于类的，但根据 构造函数、原型对象和方法的共同模式定义类样抽象通常是方便的。ECMAScript 内置对象本身遵循这样的类样模式。从 ECMAScript 2015 开始，ECMAScript 语言包括语法类定义，允许程序员简洁地定义符合内置对象使用的相同类样抽象模式的对象。
4.3.2 ECMAScript 的严格变体
ECMAScript 语言认识到某些用户可能希望限制其使用语言中某些功能的可能性。他们可能出于安全考虑，避免他们认为容易出错的功能，获得增强的错误检查，或出于其他原因。为了支持这种可能性，ECMAScript 定义了语言的严格变体。语言的严格变体排除了一些常规 ECMAScript 语言的特定语法和语义特性，并修改了某些特性的详细语义。严格变体还指定了在非严格形式的语言未指定为错误的情况下必须通过抛出错误异常来报告的其他错误条件。
ECMAScript 的严格变体通常称为语言的严格模式。严格模式的选择和 ECMAScript 严格模式语法和语义的使用明确在单个 ECMAScript 源文本 单元级别进行，如 11.2.2 中所述。由于在语法源文本单元级别选择严格模式，因此严格模式仅对该源文本单元内具有局部效果的限制。严格模式不会限制或修改必须在多个源文本单元之间一致操作的 ECMAScript 语义。完整的 ECMAScript 程序可以由严格模式和非严格模式 ECMAScript 源文本 单元组成。在这种情况下，严格模式仅在实际执行在严格模式源文本单元中定义的代码时才适用。
为了符合本规范，ECMAScript 实现必须实现完整的无限制 ECMAScript 语言和本规范定义的 ECMAScript 语言的严格变体。此外，实现必须支持将无限制和严格模式源文本单元组合成一个单一的组合程序。
4.4 术语和定义
在本文件中，适用以下术语和定义。
4.4.1 实现近似 (implementation-approximated)
一个 实现近似 设施是由外部来源全部或部分定义的，但在本规范中有推荐的理想行为。
4.4.2 实现定义 (implementation-defined)
一个 实现定义 设施是由外部来源全部或部分定义的。
4.4.3 主机定义 (host-defined)
与 实现定义 相同。
编辑说明，参见 4.2 条款。
4.4.4 类型 (type)
数据值集合，定义见
4.4.5 原始值 (primitive value)
是 Undefined、Null、Boolean、Number、BigInt、Symbol 或 String 类型中的一个成员，定义见
原始值是在语言实现的最低层直接表示的数据。
4.4.6 对象 (object)
Object 类型的成员。
对象是属性的集合，并且有一个单一的原型对象。原型可以是
4.4.7 构造函数 (constructor)
构造函数的
4.4.8 原型 (prototype)
为其他对象提供共享属性的对象。
4.4.9 普通对象 (ordinary object)
具有所有对象必须支持的基本内部方法默认行为的对象
4.4.10 特殊对象 (exotic object)
在一个或多个基本内部方法上不具有默认行为的对象
4.4.11 标准对象 (standard object)
其语义由本规范定义的对象
4.4.12 内置对象 (built-in object)
由 ECMAScript 实现指定和提供的对象
标准内置对象在本规范中定义。ECMAScript 实现可以指定和提供其他种类的内置对象。
4.4.13 未定义值 (undefined value)
当变量未被赋值时使用的原始值
4.4.14 Undefined 类型 (Undefined type)
唯一值为
4.4.15 空值 (null value)
表示故意缺少任何对象值的原始值
4.4.16 Null 类型 (Null type)
唯一值为
4.4.17 布尔值 (Boolean value)
属于
只有两个布尔值，
4.4.18 Boolean 类型 (Boolean type)
由原始值
4.4.19 Boolean 对象 (Boolean object)
属于
Boolean 对象是通过在 new 表达式中使用 Boolean
4.4.20 字符串值 (String value)
原始值，是一个
4.4.21 字符串类型 (String type)
所有可能的字符串值的集合
4.4.22 字符串对象 (String object)
4.4.23 Number 值 (Number value)
对应双精度 64 位二进制格式
Number 值是
4.4.24 Number 类型 (Number type)
所有可能的 Number 值的集合，包括特殊的“非数值” (NaN) 值、正无穷大和负无穷大
4.4.25 Number 对象 (Number object)
属于
4.4.26 无穷大 (Infinity)
表示正无穷大的 Number 值
4.4.27 NaN
表示
4.4.28 BigInt 值 (BigInt value)
对应任意精度
4.4.29 BigInt 类型 (BigInt type)
所有可能的 BigInt 值的集合
4.4.30 BigInt 对象 (BigInt object)
4.4.31 Symbol 值 (Symbol value)
表示唯一的、非字符串对象
4.4.32 Symbol 类型 (Symbol type)
所有可能的 Symbol 值的集合
4.4.33 Symbol 对象 (Symbol object)
4.4.34 函数 (function)
属于
除了它的属性之外，函数还包含可执行代码和状态，这些代码和状态决定了它在调用时的行为。函数的代码可以是 ECMAScript 编写的，也可以不是。
4.4.35 内置函数 (built-in function)
内置对象，是一个函数
内置函数的例子包括 parseInt 和 Math.exp。
4.4.36 内置构造函数 (built-in constructor)
内置函数，是一个
4.4.37 属性 (property)
对象的一部分，关联一个键（字符串值或 Symbol 值）和一个值
根据属性的形式，值可以直接表示为数据值（原始值、对象或
4.4.38 方法 (method)
作为属性值的函数
当函数作为对象的方法调用时，对象会作为其
4.4.39 内置方法 (built-in method)
作为内置函数的方法
标准内置方法在本规范中定义。
4.4.40 属性 (attribute)
定义属性某些特性的内部值
4.4.41 自有属性 (own property)
直接包含在对象中的属性
4.4.42 继承属性 (inherited property)
对象的属性，不是自有属性，但它是对象原型的属性（自有属性或继承属性）
4.5 本规范的组织结构 (Organization of This Specification)
本规范的其余部分组织如下：
第
第
第
第
第
5 符号约定
5.1 句法和词法语法
5.1.1 上下文无关文法
一个上下文无关文法由若干生成式组成。每个生成式的左侧都有一个抽象符号，称为非终结符，右侧则是一系列零个或多个非终结符和终结符符号。对于每个文法，终结符号来自指定的字母表。
链生成式是右侧有且只有一个非终结符号以及零个或多个终结符号的生成式。
从一个由单个特殊非终结符组成的句子开始，称为目标符号，给定的上下文无关文法指定了一种语言，即通过不断将序列中的任何非终结符替换为其左侧为该非终结符的生成式的右侧所能产生的终结符号的（可能是无限的）集合。
5.1.2 词法和正则表达式文法
ECMAScript 的词法文法在
除空白和注释外的输入元素构成 ECMAScript 语法文法的终结符，称为 ECMAScript 标记。这些标记是 ECMAScript 语言的 /*…*/ 的注释，不论是否跨越多行）不包含行终止符，则它同样会被丢弃；但如果
ECMAScript 的正则表达式文法在
词法和正则表达式文法的生成式通过两个冒号 “::” 作为分隔标点来区分。这两种文法共享一些生成式。
5.1.3 数值字符串文法
在
数值字符串文法的生成式通过三个冒号 “:::” 作为标点符号来区分，且从不用于解析源文本。
5.1.4 句法文法
ECMAScript 的 句法文法 在
当要将代码点流解析为 ECMAScript
解析成功时，会构造一个 解析树，这是一个以根为起点的树结构，其中每个节点是一个 解析节点。每个解析节点都是文法中某个符号的实例；它表示可以从该符号派生的源文本范围。表示整个源文本的解析树的根节点是解析的
解析器的每次调用都会实例化新的解析节点，并且在解析相同源文本时永不重用。解析节点被认为是相同的解析节点，当且仅当它们表示相同的源文本范围，是相同文法符号的实例，并且是由同一次解析器调用生成的。
多次解析相同的字符串会导致不同的解析节点。例如，考虑：
let str = "1 + 1;";
eval(str);
eval(str);每次调用 eval 都会将 str 的值转换为
句法文法的生成式通过使用一个冒号 “:” 作为标点符号来区分。
在
在某些情况下，为避免歧义，句法文法使用了泛化生成式，允许不形成有效 ECMAScript
- 使用 N 作为
目标符号 重新解析最初由 P 匹配的标记序列。如果 N 采用文法参数，则它们设置为与最初解析 P 时相同的值。 - 如果标记序列可以解析为 N 的单个实例，并且没有剩余标记，则：
- 我们将该 N 的实例（解析节点，在给定 P 的情况下是唯一的）称为“由 P 覆盖的 N”。
- N 及其派生生成式的所有早期错误规则也适用于由 P 覆盖的 N。
- 否则（如果解析失败），则为早期语法错误。
5.1.5 语法标记
5.1.5.1 终结符号
在ECMAScript语法中，一些终结符号显示为固定宽度字体。这些符号应当按照书写的样子准确出现在源文本中。以这种方式指定的所有终结符号码点都应被理解为来自基本拉丁块的适当Unicode码点，而不是来自其他Unicode范围的类似看起来的码点。终结符号中的一个码点不能通过\
在其终结符号是单个Unicode码点的语法中（即，词汇、RegExp和数值字符串语法），连续的多个固定宽度码点出现在一个生产中，是一种简单的速记，用于表示相同的码点序列，写作独立的终结符号。
例如，产生式：
是以下的简写形式：
相比之下，在句法语法中，连续的固定宽度码点构成一个单独的终结符号。
终结符号还有其他两种形式：
- 在词汇和RegExp语法中，没有常规打印表示的Unicode码点，会以"<ABBREV>"的形式显示，其中"ABBREV"是该码点或码点集的助记符。这些形式在
Unicode格式控制字符 、空白字符 和行终结符 中定义。 - 在句法语法中，某些终结符号（例如
IdentifierName 和RegularExpressionLiteral ）以斜体显示，因为它们指的是词汇语法中同名的非终结符号。
5.1.5.2 非终结符号与生产规则
非终结符号显示为斜体类型。非终结（也称为“产生式”）的定义是由被定义的非终结名称开始，后面跟着一个或多个冒号（冒号的数量表示生产所属的语法）。然后，非终结的一个或多个备选右侧在后续行中跟随。例如，句法定义：
说明非终结while，后跟一个左括号，然后是一个
说明一个
5.1.5.3 可选符号
下标后缀“opt”，可出现在终结符或非终结符之后，表示一个可选符号。包含可选符号的替代项实际上指定了两个右侧，一个省略可选元素，一个包含它。这意味着：
是一个方便的缩写：
和：
是一个方便的缩写：
反过来又是一个缩写：
因此，在这个例子中，非终结符
5.1.5.4 语法参数
一个产生式可能会被形式为“[parameters]”的下标注释参数化，它可能作为由产生式定义的非终结符号的后缀出现。“parameters”可以是单个名称或逗号分隔的名称列表。参数化的产生式是一组产生式的简写，这些产生式定义了所有参数名称的组合，这些名称由下划线前缀，并附加到参数化的非终结符号上。这意味着：
是以下的缩写:
并且：
是以下的缩写：
多个参数会产生组合数量的产生式，但并不是所有的产生式都必须在完整的语法中被引用。
产生式右侧的非终结符号的引用也可以被参数化。例如：
等同于说：
以及：
相当于：
一个非终结符的引用可能同时具有参数列表和“opt”后缀。例如：
是以下的缩写：
在右侧非终结符引用中，用“?”前缀参数名称，使得该参数值依赖于当前产生式左侧符号引用中参数名称的出现。例如：
是以下的缩写：
如果右侧的备选方案以“[+parameter]”为前缀，那么这个备选方案只在引用产生式的非终结符号时使用了指定的参数才可用。如果右侧的备选方案以“[~parameter]”为前缀，那么这个备选方案只在引用产生式的非终结符号时未使用指定的参数才可用。这意味着：
是以下的缩写：
并且：
是以下的缩写：
5.1.5.5 one of
当语法定义中的冒号后面跟着“one of”这几个词时，它们表示接下来的每一行上的终结符号都是一个替代定义。例如，ECMAScript的词法语法包含以下产生式：
这只是一个方便的缩写，完整形式为：
5.1.5.6 [empty]
如果产生式的右侧出现“[empty]”这一短语，它表示该产生式的右侧不包含任何终结符号或非终结符号。
5.1.5.7 前瞻限制
如果短语“[lookahead = seq]”出现在产生式的右侧，它表示只有当令牌序列seq是紧随其后的输入令牌序列的前缀时，才能使用该产生式。类似地，“[lookahead ∈ set]”，其中set是一个非空的有限令牌序列集合，表示只有当set中的某个元素是紧随其后的令牌序列的前缀时，才能使用该产生式。为了方便起见，该集合也可以写作非终结符，这种情况下它代表所有非终结符可以扩展到的令牌序列的集合。如果非终结符可以扩展到无限多个不同的令牌序列，则被认为是编辑错误。
这些条件可以被否定。“[lookahead ≠ seq]”表示只有当seq不是紧随其后的输入令牌序列的前缀时，才能使用包含的产生式，“[lookahead ∉ set]”表示只有当set中的没有元素是紧随其后的令牌序列的前缀时，才能使用该产生式。
例如，给定以下定义：
定义如下：
匹配字母n，后跟一个或多个十进制数字，第一个数字为偶数，或一个十进制数字，后面没有跟随另一个十进制数字。
注意，当这些短语在句法语法中使用时，可能无法明确识别紧随其后的令牌序列，因为确定后续的令牌需要知道在后续位置使用哪个词法目标符号。因此，当这些短语在句法语法中使用时，如果词法目标符号的选择可能会改变seq是否会成为生成的令牌序列的前缀，那么在前视限制中出现令牌序列seq（包括作为序列集合的一部分）被认为是编辑错误。
5.1.5.8 [no LineTerminator here]
如果在句法文法的生成式右侧出现短语“[no
表示如果在脚本中 throw 标记和
除非受限生成式禁止出现
5.1.5.9 but not
生成式的右侧可以使用短语“but not”并指示要排除的扩展来指定不允许某些扩展。例如，生成式：
意味着非终结符
5.1.5.10 描述性短语
最后，在一些列出所有替代方案不切实际的情况下，使用无衬线字体的描述性短语来描述少数非终结符号：
5.2 算法约定
该规范经常使用编号列表来指定算法中的步骤。这些算法用于精确指定 ECMAScript 语言结构的所需语义。这些算法并不意味着必须使用任何特定的实现技术。实际上，可能有更有效的算法可用于实现给定的功能。
算法可以明确地用一个有序的、逗号分隔的别名序列参数化，这些别名在算法步骤中可用于引用在该位置传入的参数。可选参数用方括号（[ , name
]）表示，与算法步骤中的必需参数没有区别。参数列表的末尾可以出现一个剩余参数，以省略号（, ...name）表示。剩余参数捕获所有在必需参数和可选参数之后提供的参数，这些参数被编入一个
算法步骤可以细分为顺序子步骤。子步骤是缩进的，并且本身可以进一步分为缩进的子步骤。用大纲编号约定来标识子步骤，第一层子步骤用小写字母标记，第二层子步骤用小写罗马数字标记。如果需要超过三个层级，这些规则将重复，第四层使用数字标签。例如：
- 顶层步骤
- 子步骤。
- 子步骤。
- 子子步骤。
- 子子子步骤
- 子子子子步骤
- 子子子子子步骤
- 子子子子步骤
- 子子子步骤
- 子子步骤。
步骤或子步骤可以作为一个“if”谓词编写，条件化其子步骤。在这种情况下，只有当谓词为真时，子步骤才会被应用。如果步骤或子步骤以“else”一词开头，它是一个谓词，是与同一层级前一个“if”谓词步骤的否定。
步骤可以指定其子步骤的迭代应用。
以“Assert（断言）:”开头的步骤断言其算法的不变条件。这种断言用来明确那些否则会是隐含的算法不变性。这样的断言不增加额外的语义要求，因此实现无需检查。它们仅用于澄清算法。
算法步骤可以使用“Let x be someValue”的形式声明任何值的命名别名。这些别名类似于引用，x和someValue都指向相同的底层数据，对任何一个的修改都对双方可见。如果算法步骤想要避免这种类似引用的行为，应该明确地复制右侧值：“Let x be a copy of someValue”创建了someValue的一个浅拷贝。
一旦声明，别名可以在任何后续步骤中被引用，并且不能从别名声明之前的步骤中被引用。别名可以使用“Set x to someOtherValue”的形式进行修改。
5.2.1 抽象操作
为了便于在本规范的多个部分中使用，一些算法被称为抽象操作，它们被命名并以参数化的函数形式编写，以便可以从其他算法中通过名称引用它们。抽象操作通常使用函数应用风格引用，如 OperationName(arg1, arg2)。一些抽象操作被视为类似类的规范抽象中多态分派的方法。这种类似方法的抽象操作通常使用方法应用风格引用，例如 someValue.OperationName(arg1, arg2)。
5.2.2 语法指导操作
一个语法指导操作是一个命名操作，其定义包括多个算法，每个算法都与ECMAScript语法之一的一个或多个产生式相关联。具有多个替代定义的产生式通常会为每个替代定义有一个独特的算法。当一个算法与一个语法产生式相关联时，它可以引用产生式替代的终结符和非终结符，就好像它们是算法的参数一样。在这种方式下使用时，非终结符引用在解析源文本时匹配的实际替代定义。由语法产生式匹配的源文本或由其衍生的
当一个算法与一个产生式替代相关联时，该替代通常显示时不包括任何“[ ]”语法注释。这样的注释只应影响替代的语法识别，对替代的相关语义没有影响。
语法指导操作通过使用下列算法中的步骤
- 让status为SyntaxDirectedOperation of
SomeNonTerminal 。 - 让someParseNode为一些源文本的解析。
- 执行someParseNode的SyntaxDirectedOperation。
- 带参数
"value" 执行someParseNode的SyntaxDirectedOperation。
除非另有明确规定，所有
但是
运行时语义：
5.2.3 运行时语义
需要在运行时调用以指定语义的算法称为运行时语义。运行时语义由
5.2.3.1 完成（completionRecord）
抽象操作完成接受参数completionRecord（一个
5.2.3.2 抛出异常
算法步骤中提到抛出异常的，如：
- 抛出一个
TypeError 异常。
意味着与以下内容相同：
- 返回
ThrowCompletion (新创建的TypeError 对象)。
5.2.3.3 ReturnIfAbrupt
算法步骤中提到或等同于以下内容：
ReturnIfAbrupt (argument)。
意味着：
Assert ：argument 是一个Completion Record 。- 如果 argument 是一个
abrupt completion ，返回Completion (argument)。 - 否则，将 argument 设置为 argument.[[Value]]。
算法步骤中提到或等同于：
ReturnIfAbrupt (AbstractOperation())。
意味着：
- 让 hygienicTemp 是 AbstractOperation()。
Assert ：hygienicTemp 是一个Completion Record 。- 如果 hygienicTemp 是一个
abrupt completion ，返回Completion (hygienicTemp)。 - 否则，将 hygienicTemp 设置为 hygienicTemp.[[Value]]。
hygienicTemp 是短暂的，仅在涉及 ReturnIfAbrupt 的步骤中可见。
算法步骤中提到或等同于：
- 让 result 是 AbstractOperation(
ReturnIfAbrupt (argument))。
意味着：
Assert ：argument 是一个Completion Record 。- 如果 argument 是一个
abrupt completion ，返回Completion (argument)。 - 否则，将 argument 设置为 argument.[[Value]]。
- 让 result 是 AbstractOperation(argument)。
5.2.3.4 ReturnIfAbrupt 简写
在?表示应当应用
- ? OperationName().
等同于以下步骤：
ReturnIfAbrupt (OperationName())。
同样，对于方法应用风格，步骤：
- ? someValue.OperationName().
等同于：
ReturnIfAbrupt (someValue.OperationName())。
同样地，前缀!用来表示以下对抽象或
- 让 val 是 ! OperationName().
等同于以下步骤：
!或?：
- 执行 ! SyntaxDirectedOperation of
NonTerminal 。
5.2.3.5 隐式正常完成
在声明返回
- 当直接返回应用
Completion 、NormalCompletion 或ThrowCompletion 的结果时 - 当直接返回构建一个
完成记录 的结果时
如果通过任何其他方式从这样的抽象操作中返回
- 返回
true 。
意味着与任何一种
- 返回
NormalCompletion (true )。
或
- 让completion是
NormalCompletion (true )。 - 返回
Completion (completion)。
或
- 返回
完成记录 { [[Type]]:normal , [[Value]]:true , [[Target]]:empty }。
注意，通过
- 返回 ? completion。
以下示例将是一个编辑错误，因为在该步骤中没有注明正在返回
- 让completion是
NormalCompletion (true )。 - 返回completion。
5.2.4 静态语义
无上下文语法并不足以表达所有定义流式输入元素是否形成可评估的 ECMAScript
静态语义规则具有名称，并通常使用算法定义。命名的静态语义规则与语法产生式相关联，具有多个备选定义的产生式通常对每个适用的命名静态语义规则有一个单独的算法。
静态语义规则的一种特殊类型是早期错误规则。
5.2.5 数学运算
本规范参考以下数值类型：
- 数学值：任意实数，作为默认的数值类型使用。
- 扩展数学值：
数学值 加上 +∞ 和 -∞。 - 数字：IEEE 754-2019 双精度浮点数值。
参见 IEEE 754-2019 。 - BigInts：
ECMAScript 语言值 ，表示与整数整数 一一对应的任意整数。
在本规范的术语中，数值使用下标后缀来区分不同的数值类型。下标 𝔽 表示数字（Numbers），下标 ℤ 表示大整数（BigInts）。没有下标后缀的数值指代
数值运算符（如 +、×、= 和 ≥）根据操作数的类型确定其操作。当应用于
一般来说，当本规范提到数值时，例如“y 的长度”或“由四位十六进制数字表示的
不定义混合类型操作数（例如数字和
本规范中大多数数值以十进制表示；同时也使用形如 0x 后跟数字 0-9 或 A-F 的十六进制值。
当本规范中使用术语 整数 时，指的是在
本文档中对
数学函数
数学函数
记法 “
短语 "将 x 夹在 lower 和 upper 之间"（其中 x 是
数学函数
数学函数
数学函数
从下界 a 到上界 b 的 区间 是可能是无限的、可能为空的、相同数值类型的数值集合。每个边界都将描述为包含或排除，但不会同时包含。有四种类型的区间，如下所示：
从 a（包含）到 b（包含）的区间 ，也称为从 a 到 b 的 包含区间，包括所有 x 的相同数值类型，使得 a ≤ x ≤ b，但不包括其他值。从 a（包含）到 b（排除）的区间 ，包括所有 x 的相同数值类型，使得 a ≤ x < b，但不包括其他值。从 a（排除）到 b（包含）的区间 ，包括所有 x 的相同数值类型，使得 a < x ≤ b，但不包括其他值。从 a（排除）到 b（排除）的区间 ，包括所有 x 的相同数值类型，使得 a < x < b，但不包括其他值。
例如，从 1（包含）到 2（排除）的
5.2.6 值表示法
在本规范中，Function.prototype.apply 或 let n = 42; 区分开来。
5.2.7 身份
在本规范中，规范值和
从本规范的角度来看，“is”一词用于比较两个值是否相等，例如“如果bool为
从 ECMAScript 语言的角度来看，语言值使用
对于规范值，没有规范身份的值包括但不限于：
规范身份对于所有
6 ECMAScript 数据类型和值
本规范中的算法操作值，每个值都有一个关联的类型。可能的值类型正是本条款中定义的那些类型。类型进一步分为
在本规范中，“Type(x)”表示“x的类型”，其中“类型”指的是本条款中定义的ECMAScript语言和规范类型。
6.1 ECMAScript 语言类型
ECMAScript 语言类型对应于由 ECMAScript 程序员直接使用 ECMAScript 语言操作的值。ECMAScript 语言类型包括 Undefined、Null、Boolean、String、Symbol、Number、BigInt 和 Object。一个ECMAScript 语言值是由 ECMAScript 语言类型特征化的值。
6.1.1 Undefined 类型
Undefined 类型恰好有一个值，称为
6.1.2 Null 类型
Null 类型恰好有一个值，称为
6.1.3 Boolean 类型
Boolean 类型表示具有两个值的逻辑实体，称为
6.1.4 String 类型
String 类型是所有有序序列的集合，这些序列由零个或多个 16
位无符号
不解释 String 内容的 ECMAScript 操作不应用进一步的语义。对解释 String 值的操作将每个元素视为单个 UTF-16 代码单元。然而，ECMAScript 不限制这些代码单元的值或关系，因此进一步解释 String 内容为 UTF-16 编码的 Unicode 代码点序列的操作必须考虑到格式不正确的子序列。这些操作对于每个数值位于从 0xD800 到 0xDBFF（由 Unicode 标准定义为leading surrogate，或更正式地称为high-surrogate code unit）的代码单元，以及每个数值位于从 0xDC00 到 0xDFFF（定义为trailing surrogate，或更正式地称为low-surrogate code unit）的代码单元使用以下规则：
- 一个既不是前导代理对也不是后继代理对的代码单元，将被解释为具有相同值的代码点。
- 两个代码单元的序列，其中第一个代码单元 c1 是前导代理对，第二个代码单元 c2 是后继代理对，称为代理对，解释为代码点的值为 (c1 - 0xD800) × 0x400 + (c2 - 0xDC00) + 0x10000。（参见11.1.3）
- 一个是前导代理对或后继代理对的代码单元，但不是代理对的一部分，将被解释为具有相同值的代码点。
函数 String.prototype.normalize（参见22.1.3.15）可以用来显式标准化一个字符串值。String.prototype.localeCompare（参见22.1.3.12）在内部标准化字符串值，但其他操作不会隐式地标准化它们操作的字符串。操作结果除非另有说明，否则不受语言和/或地区的影响。
这种设计背后的理念是为了保持字符串的实现尽可能简单和高效。如果ECMAScript源代码文本处于规范形式C，只要它们不包含任何Unicode转义序列，字符串字面值也保证是标准化的。
在这个规范中，“字符串连接 A、B 等...”（每个参数是一个字符串值、代码单元或代码单元的序列）表示的是一个字符串值，其代码单元的序列是每个参数（按顺序）的代码单元的连接（按顺序）。
短语“从 inclusiveStart 到 exclusiveEnd 的 子字符串”（其中 S 是一个字符串值或代码单元序列，而 inclusiveStart 和 exclusiveEnd 是整数）表示由 S 的连续代码单元组成的字符串值，开始于索引 inclusiveStart 并在索引 exclusiveEnd 之前立即结束（当 inclusiveStart = exclusiveEnd 时为空字符串）。如果省略了“to”后缀，则使用 S 的长度作为 exclusiveEnd 的值。
短语“ASCII 单词字符”表示以下字符串值，它仅由 Unicode 基本拉丁语块中的每个字母和数字以及
U+005F（下划线）组成：
出于历史原因，它对各种算法具有重要意义。
6.1.4.1 StringIndexOf ( string, searchValue, fromIndex )
抽象操作 StringIndexOf 接受参数 string（一个字符串）、searchValue（一个字符串）和 fromIndex
（一个非负
如果 searchValue 是空字符串且 fromIndex ≤ string 的长度，该算法返回 fromIndex。空字符串实际上在字符串中的每个位置都能找到，包括在最后一个码位之后。
如果 fromIndex 加上 searchValue 的长度大于 string 的长度，该算法总是返回 -1。
6.1.5 符号类型（Symbol Type）
符号类型 是可以用作对象属性键的所有非字符串值的集合（
每个可能的符号值都是唯一且不可变的。
每个符号值不可变地持有一个关联的值，称为 [[Description]]，它要么是
6.1.5.1 众所周知的符号（Well-Known Symbols）
众所周知的符号是本规范算法明确引用的内建符号值。它们通常用作属性的键，这些属性的值作为规范算法的扩展点。除非另有说明，否则众所周知的符号值在所有
在本规范中，一个众所周知的符号用 @@name 的形式表示，其中“name”是
| 规范名称 | [[Description]] | 值和用途 |
|---|---|---|
| @@asyncIterator |
|
一个方法，返回对象的默认异步迭代器。由for-await-of语句的语义调用。
|
| @@hasInstance |
|
一个方法，确定构造函数对象是否将某个对象识别为其实例之一。由instanceof运算符的语义调用。
|
| @@isConcatSpreadable |
|
一个布尔值属性，如果为true，表示对象应通过Array.prototype.concat |
| @@iterator |
|
一个方法，返回对象的默认迭代器。由for-of语句的语义调用。 |
| @@match |
|
一个正则表达式方法，将正则表达式与字符串匹配。由String.prototype.match |
| @@matchAll |
|
一个正则表达式方法，返回一个迭代器，该迭代器生成正则表达式与字符串匹配的所有结果。由String.prototype.matchAll |
| @@replace |
|
一个正则表达式方法，替换字符串中的匹配子字符串。由String.prototype.replace |
| @@search |
|
一个正则表达式方法，返回匹配正则表达式的字符串中的索引。由String.prototype.search |
| @@species |
|
一个函数值属性，是用于创建派生对象的构造函数。 |
| @@split |
|
一个正则表达式方法，在匹配正则表达式的索引处分割字符串。由String.prototype.split |
| @@toPrimitive |
|
一个方法，将对象转换为相应的原始值。由 |
| @@toStringTag |
|
一个字符串值属性，用于创建对象的默认字符串描述。由内建方法Object.prototype.toString |
| @@unscopables |
|
一个对象值属性，其自身和继承的属性名称是从相关对象的with环境绑定中排除的属性名称。
|
6.1.6 数字类型（Numeric Types）
ECMAScript 有两种内建的数字类型：Number 和 BigInt。以下
由于数值类型通常不能在不损失精度或截断的情况下相互转换，ECMAScript语言不提供这些类型之间的隐式转换。在调用需要另一种类型的函数时，程序员必须显式调用 Number 和
BigInt 函数进行类型转换。
ECMAScript 的早期和后续版本为某些运算符提供了隐式数值转换，这可能会损失精度或
6.1.6.1 数字类型（The Number Type）
数字类型（Number type）具有精确的
18,437,736,874,454,810,627
（即 NaN 产生。）在一些实现中，外部代码可能能够检测到各种不同的非数值，但这种行为是
还有另外两个特殊值，分别称为 +Infinity（或简单地
Infinity）和 -Infinity 产生。）
其余的 18,437,736,874,454,810,624（即
注意，这里有一个 +0（或简单地 0）和 -0 产生。）
18,437,736,874,454,810,622（即
18,428,729,675,200,069,632（即
其中，s 可以是 1 或 -1，m 是一个
剩余的 9,007,199,254,740,990（即
其中，s 可以是 1 或 -1，m 是一个
注意，在 Number 类型中，所有不大于 253 的正整数和负整数都可以表示。整数 0 在 Number
类型中有两种表示形式：
一个
一些 ECMAScript 运算符只处理特定范围内的
6.1.6.1.1 Number::unaryMinus ( x )
抽象操作 Number::unaryMinus 接受参数 x（一个 Number），并返回一个 Number。调用时执行以下步骤：
- 如果 x 是
NaN ，则返回NaN 。 - 返回取反后的结果 x；即具有相同大小但相反符号的 Number。
6.1.6.1.2 Number::bitwiseNOT ( x )
抽象操作 Number::bitwiseNOT 接受参数 x（一个 Number），并返回一个
6.1.6.1.3 Number::exponentiate ( base, exponent )
抽象操作 Number::exponentiate 接受参数 base（一个 Number）和 exponent（一个 Number），并返回一个
Number。它返回一个
- 如果 exponent 是
NaN ，则返回NaN 。 - 如果 exponent 是
+0 𝔽 或-0 𝔽，则返回1 𝔽。 - 如果 base 是
NaN ，则返回NaN 。 - 如果 base 是
+∞ 𝔽，则- 如果 exponent >
+0 𝔽，则返回+∞ 𝔽。否则，返回+0 𝔽。
- 如果 exponent >
- 如果 base 是
-∞ 𝔽，则- 如果 exponent >
+0 𝔽，那么- 如果 exponent 是奇数的
integral Number ，则返回-∞ 𝔽。否则，返回+∞ 𝔽。
- 如果 exponent 是奇数的
- 否则，
- 如果 exponent 是奇数的
integral Number ，则返回-0 𝔽。否则，返回+0 𝔽。
- 如果 exponent 是奇数的
- 如果 exponent >
- 如果 base 是
+0 𝔽，则- 如果 exponent >
+0 𝔽，则返回+0 𝔽。否则，返回+∞ 𝔽。
- 如果 exponent >
- 如果 base 是
-0 𝔽，则- 如果 exponent >
+0 𝔽，那么- 如果 exponent 是奇数的
integral Number ，则返回-0 𝔽。否则，返回+0 𝔽。
- 如果 exponent 是奇数的
- 否则，
- 如果 exponent 是奇数的
integral Number ，则返回-∞ 𝔽。否则，返回+∞ 𝔽。
- 如果 exponent 是奇数的
- 如果 exponent >
Assert : base 是有限数，并且不是+0 𝔽 或-0 𝔽。- 如果 exponent 是
+∞ 𝔽，则 - 如果 exponent 是
-∞ 𝔽，则 Assert : exponent 是finite ，并且不是+0 𝔽 或-0 𝔽。- 如果 base <
-0 𝔽，并且 exponent 不是一个integral Number ，则返回NaN 。 - 返回一个表示将
ℝ (base) 的ℝ (exponent) 次幂的结果的implementation-approximated 数值。
当 base 是 ** exponent 的结果与
6.1.6.1.4 Number::multiply ( x, y )
抽象操作 Number::multiply 接受参数 x（一个 Number）和 y（一个 Number），返回一个 Number。它根据
6.1.6.1.5 Number::divide ( x, y )
抽象操作 Number::divide 接受参数 x（一个 Number）和 y（一个 Number），返回一个 Number。
它根据
- 如果 x 是
NaN 或者 y 是NaN ，返回NaN 。 - 如果 x 是
+∞ 𝔽 或者-∞ 𝔽，则- 如果 y 是
+∞ 𝔽 或者-∞ 𝔽，返回NaN 。 - 如果 y 是
+0 𝔽 或者 y >+0 𝔽，返回 x。 - 返回 -x。
- 如果 y 是
- 如果 y 是
+∞ 𝔽，则- 如果 x 是
+0 𝔽 或者 x >+0 𝔽，返回+0 𝔽。 否则，返回-0 𝔽。
- 如果 x 是
- 如果 y 是
-∞ 𝔽，则- 如果 x 是
+0 𝔽 或者 x >+0 𝔽，返回-0 𝔽。 否则，返回+0 𝔽。
- 如果 x 是
- 如果 x 是
+0 𝔽 或者-0 𝔽，则- 如果 y 是
+0 𝔽 或者-0 𝔽，返回NaN 。 - 如果 y >
+0 𝔽， 返回 x。 - 返回 -x。
- 如果 y 是
- 如果 y 是
+0 𝔽，则- 如果 x >
+0 𝔽， 返回+∞ 𝔽。否则，返回-∞ 𝔽。
- 如果 x >
- 如果 y 是
-0 𝔽，则- 如果 x >
+0 𝔽， 返回-∞ 𝔽。否则，返回+∞ 𝔽。
- 如果 x >
- 返回
𝔽 (ℝ (x) /ℝ (y)).
6.1.6.1.6 Number::remainder ( n, d )
抽象操作 Number::remainder 接受参数 n（一个 Number）和 d（一个 Number），返回一个 Number。 它返回其操作数的隐含除法的余数，其中 n 是被除数，d 是除数。调用时执行以下步骤：
在 C 和 C++ 中，取余运算符只接受整数操作数；在 ECMAScript 中，它也接受浮点操作数。
% 运算符计算的“余数”操作不同，后者由 % 以类似于 Java 6.1.6.1.7 Number::add ( x, y )
抽象操作 Number::add 接受参数 x（一个 Number）和 y（一个 Number），返回一个
Number。它根据
6.1.6.1.8 Number::subtract ( x, y )
抽象操作 Number::subtract 接受参数 x（一个 Number）和 y（一个 Number），返回一个 Number。它执行减法运算，生成其操作数的差；x 是被减数，y 是减数。调用时执行以下步骤：
- 返回
Number::add (x,Number::unaryMinus (y))。
总是有 x - y 的结果与 x + (-y) 相同。
6.1.6.1.9 Number::leftShift ( x, y )
抽象操作 Number::leftShift 接受参数 x（一个 Number）和 y（一个 Number），返回一个整数 Number。调用时执行以下步骤：
6.1.6.1.10 Number::signedRightShift ( x, y )
抽象操作 Number::signedRightShift 接受参数 x（一个 Number）和 y（一个 Number），返回一个整数 Number。调用时执行以下步骤：
6.1.6.1.11 Number::unsignedRightShift ( x, y )
抽象操作 Number::unsignedRightShift 接受参数 x（一个 Number）和 y（一个 Number），返回一个整数 Number。调用时执行以下步骤：
6.1.6.1.12 Number::lessThan ( x, y )
抽象操作 Number::lessThan 接受参数 x（一个 Number）和 y（一个 Number），返回一个布尔值或
6.1.6.1.13 Number::equal ( x, y )
抽象操作 Number::equal 接受参数 x（一个 Number）和 y（一个 Number），返回一个布尔值。调用时执行以下步骤：
- 如果 x 是
NaN ，则返回false 。 - 如果 y 是
NaN ，则返回false 。 - 如果 x 等于 y，则返回
true 。 - 如果 x 是
+0 𝔽 并且 y 是-0 𝔽，则返回true 。 - 如果 x 是
-0 𝔽 并且 y 是+0 𝔽，则返回true 。 - 返回
false 。
6.1.6.1.14 Number::sameValue ( x, y )
抽象操作 Number::sameValue 接受参数 x（一个 Number）和 y（一个 Number），返回一个布尔值。调用时执行以下步骤：
- 如果 x 是
NaN 并且 y 是NaN ，则返回true 。 - 如果 x 是
+0 𝔽 并且 y 是-0 𝔽，则返回false 。 - 如果 x 是
-0 𝔽 并且 y 是+0 𝔽，则返回false 。 - 如果 x 等于 y，则返回
true 。 - 返回
false 。
6.1.6.1.15 Number::sameValueZero ( x, y )
抽象操作 Number::sameValueZero 接受参数 x（一个 Number）和 y（一个 Number），返回一个布尔值。调用时执行以下步骤：
- 如果 x 是
NaN 并且 y 是NaN ，则返回true 。 - 如果 x 是
+0 𝔽 并且 y 是-0 𝔽，则返回true 。 - 如果 x 是
-0 𝔽 并且 y 是+0 𝔽，则返回true 。 - 如果 x 等于 y，则返回
true 。 - 返回
false 。
6.1.6.1.16 Number::NumberBitwiseOp ( op, x, y )
抽象操作 Number::NumberBitwiseOp 接受参数 op（&、^ 或
|）、x（一个 Number）和 y（一个 Number），返回一个
- 令 lnum 为 !
ToInt32 (x). - 令 rnum 为 !
ToInt32 (y). - 令 lbits 为表示
ℝ (lnum) 的 32 位二进制补码位字符串。 - 令 rbits 为表示
ℝ (rnum) 的 32 位二进制补码位字符串。 - 如果 op 是
&，则- 令 result 为对 lbits 和 rbits 执行按位与操作的结果。
- 否则，如果 op 是
^，则- 令 result 为对 lbits 和 rbits 执行按位异或（XOR）操作的结果。
- 否则，
Assert ：断言 op 是|。- 令 result 为对 lbits 和 rbits 执行按位或操作的结果。
- 返回由 32 位二进制补码位字符串 result 表示的
Number value for 的integer 。
6.1.6.1.17 Number::bitwiseAND ( x, y )
抽象操作 Number::bitwiseAND 接受参数 x（一个 Number）和 y（一个 Number），返回一个
- 返回
NumberBitwiseOp (&, x, y).
6.1.6.1.18 Number::bitwiseXOR ( x, y )
抽象操作 Number::bitwiseXOR 接受参数 x（一个 Number）和 y（一个 Number），返回一个
- 返回
NumberBitwiseOp (^, x, y).
6.1.6.1.19 Number::bitwiseOR ( x, y )
抽象操作 Number::bitwiseOR 接受参数 x（一个 Number）和 y（一个 Number），返回一个
- 返回
NumberBitwiseOp (|, x, y).
6.1.6.1.20 Number::toString ( x, radix )
抽象操作 Number::toString 接受参数 x（一个数字）和 radix（一个在 2 到 36 之间的整数），并返回一个字符串。它使用以
radix 为基数的进位制系统将 x 表示为字符串。使用基数 r 表示数字时所用的数字取自
- 如果 x 是
NaN ，返回"NaN" 。 - 如果 x 是
+0 𝔽 或-0 𝔽，返回"0" 。 - 如果 x <
-0 𝔽，返回字符串连接 的"-" 和Number::toString (-x, radix)。 - 如果 x 是
+∞ 𝔽，返回"Infinity" 。 - 令
n、k 和 s 为
整数 ，使得 k ≥ 1，radixk - 1 ≤ s < radixk，𝔽 (s × radixn - k) 是 x，并且 k 尽可能小。注意，k 是使用基数 radix 表示 s 的数字个数，s 不能被 radix 整除，并且 s 的最低有效位不一定由这些条件唯一确定。 - 如果 radix ≠ 10 或 n 在
包含区间 从 -5 到 21，那么 - 注意：在这种情况下，输入将使用科学 E 表示法表示，例如
1.2e+3。 断言 ：radix 是 10。- 如果 n < 0，那么
- 令 exponentSign 为代码单元 0x002D (HYPHEN-MINUS)。
- 否则，
- 令 exponentSign 为代码单元 0x002B (PLUS SIGN)。
- 如果 k = 1，那么
- 返回
字符串连接 ：- 十进制表示的 s 的最高有效位的代码单元
- 代码单元 0x002E (FULL STOP)
- 十进制表示的 s 的剩余 k - 1 位数字的代码单元
- 代码单元 0x0065 (LATIN SMALL LETTER E)
- exponentSign
- 十进制表示的
abs (n - 1)
ECMAScript 的实现者可能会发现 David M. Gay 撰写的关于浮点数二进制到十进制转换的论文和代码很有用：
Gay, David M. 正确舍入的二进制-十进制和十进制-二进制转换。数值分析，手稿 90-10。AT&T 贝尔实验室（新泽西州默里山）。1990 年 11 月 30 日。
可在
http://ampl.com/REFS/abstracts.html#rounding
获取。
相关代码可在
http://netlib.sandia.gov/fp/dtoa.c 和
http://netlib.sandia.gov/fp/g_fmt.c 获取，并且可能在各个
netlib 镜像站点上找到。
6.1.6.2 BigInt 类型
BigInt 类型 表示一个
6.1.6.2.1 BigInt::unaryMinus ( x )
抽象操作 BigInt::unaryMinus 接受参数 x（一个 BigInt）并返回一个 BigInt。它在被调用时执行以下步骤：
- 如果 x 是
0 ℤ，返回0 ℤ。 - 返回 -x。
6.1.6.2.2 BigInt::bitwiseNOT ( x )
抽象操作 BigInt::bitwiseNOT 接受参数 x（一个 BigInt）并返回一个 BigInt。 它返回 x 的按位取反。它在被调用时执行以下步骤：
- 返回 -x -
1 ℤ。
6.1.6.2.3 BigInt::exponentiate ( base, exponent )
抽象操作 BigInt::exponentiate 接受参数 base（一个 BigInt）和 exponent（一个 BigInt），并返回一个包含 BigInt 的正常完成或抛出完成。它在被调用时执行以下步骤：
- 如果 exponent <
0 ℤ，抛出一个RangeError 异常。 - 如果 base 是
0 ℤ 且 exponent 是0 ℤ，返回1 ℤ。 - 返回 base 的 exponent 次方。
6.1.6.2.4 BigInt::multiply ( x, y )
抽象操作 BigInt::multiply 接受参数 x（一个 BigInt）和 y（一个 BigInt）并返回一个 BigInt。它在被调用时执行以下步骤：
- 返回 x × y。
6.1.6.2.5 BigInt::divide ( x, y )
抽象操作 BigInt::divide 接受参数 x（一个 BigInt）和 y（一个 BigInt），并返回一个包含 BigInt 的正常完成或抛出完成。它在被调用时执行以下步骤：
6.1.6.2.6 BigInt::remainder ( n, d )
抽象操作 BigInt::remainder 接受参数 n（一个 BigInt）和 d（一个 BigInt），并返回一个
6.1.6.2.7 BigInt::add ( x, y )
抽象操作 BigInt::add 接受参数 x（一个 BigInt）和 y（一个 BigInt）并返回一个 BigInt。它在被调用时执行以下步骤：
- 返回 x + y。
6.1.6.2.8 BigInt::subtract ( x, y )
抽象操作 BigInt::subtract 接受参数 x（一个 BigInt）和 y（一个 BigInt）并返回一个 BigInt。它在被调用时执行以下步骤：
- 返回 x - y。
6.1.6.2.9 BigInt::leftShift ( x, y )
抽象操作 BigInt::leftShift 接受参数 x（一个 BigInt）和 y（一个 BigInt）并返回一个 BigInt。它在被调用时执行以下步骤：
6.1.6.2.10 BigInt::signedRightShift ( x, y )
抽象操作 BigInt::signedRightShift 接受参数 x（一个 BigInt）和 y（一个 BigInt）并返回一个 BigInt。它在被调用时执行以下步骤：
- 返回
BigInt::leftShift (x, -y).
6.1.6.2.11 BigInt::unsignedRightShift ( x, y )
抽象操作 BigInt::unsignedRightShift 接受参数 x（一个 BigInt）和 y（一个 BigInt）并返回一个
- 抛出一个
TypeError 异常。
6.1.6.2.12 BigInt::lessThan ( x, y )
抽象操作 BigInt::lessThan 接受参数 x（一个 BigInt）和 y（一个 BigInt）并返回一个布尔值。它在被调用时执行以下步骤：
6.1.6.2.13 BigInt::equal ( x, y )
抽象操作 BigInt::equal 接受参数 x（一个 BigInt）和 y（一个 BigInt）并返回一个布尔值。它在被调用时执行以下步骤：
6.1.6.2.14 BinaryAnd ( x, y )
抽象操作 BinaryAnd 接受参数 x（0 或 1）和 y（0 或 1）并返回 0 或 1。它在被调用时执行以下步骤：
- 如果 x = 1 且 y = 1，返回 1。
- 否则，返回 0。
6.1.6.2.15 BinaryOr ( x, y )
抽象操作 BinaryOr 接受参数 x（0 或 1）和 y（0 或 1）并返回 0 或 1。它在被调用时执行以下步骤：
- 如果 x = 1 或 y = 1，返回 1。
- 否则，返回 0。
6.1.6.2.16 BinaryXor ( x, y )
抽象操作 BinaryXor 接受参数 x（0 或 1）和 y（0 或 1）并返回 0 或 1。它在被调用时执行以下步骤：
- 如果 x = 1 且 y = 0，返回 1。
- 否则如果 x = 0 且 y = 1，返回 1。
- 否则，返回 0。
6.1.6.2.17 BigInt位运算 ( op, x, y )
抽象操作 BigInt位运算 接受参数 op（&、
^ 或 |）、x（一个 BigInt）和 y（一个 BigInt）并返回一个
BigInt。它在被调用时执行以下步骤：
- 将 x 设置为
ℝ (x)。 - 将 y 设置为
ℝ (y)。 - 设 result 为 0。
- 设 shift 为 0。
- 重复，直到 (x = 0 或 x = -1) 和 (y = 0 或 y = -1)，
- 如果 op 是
&，那么 - 否则如果 op 是
|，那么 - 否则
- 如果 tmp ≠ 0，那么
- 将 result 设置为 result - 2shift。
- 注意：这扩展了符号位。
- 返回
BigInt 值 for result。
6.1.6.2.18 BigInt::bitwiseAND ( x, y )
抽象操作 BigInt::bitwiseAND 接受参数 x（一个 BigInt）和 y（一个 BigInt）并返回一个 BigInt。它在调用时执行以下步骤：
- 返回
BigIntBitwiseOp (&, x, y)。
6.1.6.2.19 BigInt::bitwiseXOR ( x, y )
抽象操作 BigInt::bitwiseXOR 接受参数 x（一个 BigInt）和 y（一个 BigInt）并返回一个 BigInt。它在调用时执行以下步骤：
- 返回
BigIntBitwiseOp (^, x, y)。
6.1.6.2.20 BigInt::bitwiseOR ( x, y )
抽象操作 BigInt::bitwiseOR 接受参数 x（一个 BigInt）和 y（一个 BigInt）并返回一个 BigInt。它在调用时执行以下步骤：
- 返回
BigIntBitwiseOp (|, x, y)。
6.1.6.2.21 BigInt::toString ( x, radix )
抽象操作 BigInt::toString 接受参数 x（一个 BigInt）和 radix（一个在 2 到 36 之间的整数）并返回一个字符串。它使用基数
radix 将 x 表示为字符串。使用基数 r 表示 BigInt 的数字取自
- 如果 x <
0 ℤ，返回字符串连接 的"-" 和BigInt::toString (-x, radix)。 - 返回使用基数 radix 表示 x 的字符串值。
6.1.7 对象类型
每个 对象类型 的实例，也简称为“一个对象”，表示一个属性的集合。每个属性要么是一个数据属性，要么是一个访问器属性：
-
一个 数据属性 将一个键值与一个
ECMAScript 语言值 和一个布尔属性集合关联起来。 -
一个 访问器属性
将一个键值与一个或两个访问器函数以及一个布尔属性集合关联起来。访问器函数用于存储或检索与该属性相关联的
ECMAScript 语言值 。
对象的属性使用属性键唯一标识。一个 属性键
要么是一个字符串，要么是一个符号。所有字符串和符号，包括空字符串，都可以作为属性键。一个 属性名 是一个
一个 整数索引 是一个
属性键用于访问属性和它们的值。属性访问有两种类型：获取 和 设置，分别对应于值的检索和赋值。通过获取和设置访问的属性包括 自有属性 和 继承属性。继承属性可能是关联对象的自有属性或继承属性。每个对象的自有属性必须具有与其他自有属性不同的键值。
所有对象在逻辑上都是属性的集合，但有多种形式的对象，它们的属性访问和操作语义不同。请参见
此外，一些对象是可调用的；这些被称为函数或
6.1.7.1 属性属性
属性用于在本规范中定义和解释对象属性的状态，如
| 属性名称 | 存在的属性类型 | 值域 | 默认值 | 描述 |
|---|---|---|---|---|
| [[Value]] |
|
|
|
通过获取属性访问检索到的值。 |
| [[Writable]] |
|
布尔值 |
|
如果为 |
| [[Get]] |
|
对象或 |
|
如果值 |
| [[Set]] |
|
对象或 |
|
如果值 |
| [[Enumerable]] |
|
一个布尔值 |
|
如果 |
| [[Configurable]] |
|
一个布尔值 |
|
如果 |
6.1.7.2 对象内部方法和内部槽
在 ECMAScript 中，对象的实际语义是通过称为 内部方法 的算法指定的。每个 ECMAScript 引擎中的对象都与一组内部方法相关联，这些方法定义了其运行时行为。这些内部方法不是 ECMAScript 语言的一部分。它们纯粹是为了说明目的而由本规范定义的。然而，ECMAScript 实现中的每个对象必须按照与其相关联的内部方法指定的行为方式行事。实现的具体方式由实现决定。
内部方法名称是多态的。这意味着不同的对象值在调用相同的内部方法名称时可能会执行不同的算法。实际调用内部方法的对象是调用的“目标”。如果在运行时，算法的实现尝试使用对象不支持的内部方法，则会抛出
内部槽对应于与对象相关联并被各种 ECMAScript 规范算法使用的内部状态。内部槽不是对象属性，也不会被继承。
根据特定的内部槽规范，这种状态可能由任何
所有对象都有一个名为 [[PrivateElements]] 的内部槽，它是一个
内部方法和内部槽在本规范中使用双括号 [[ ]] 括起来的名称进行标识。
一个 普通对象 是满足以下所有条件的对象：
-
对于
表 4 中列出的内部方法，对象使用10.1 中定义的那些。 -
如果对象具有 [[Call]] 内部方法，它使用
10.2.1 或10.3.1 中定义的其中之一。 -
如果对象具有 [[Construct]] 内部方法，它使用
10.2.2 或10.3.2 中定义的其中之一。
一个 外来对象 是一个不是
本规范通过这些对象的内部方法识别不同种类的
除了其参数外，内部方法总是可以访问作为方法调用目标的对象。
内部方法隐式返回一个
| 内部方法 | 签名 | 描述 |
|---|---|---|
| [[GetPrototypeOf]] | ( ) → Object | Null |
确定为该对象提供继承属性的对象。 |
| [[SetPrototypeOf]] | (Object | Null) → Boolean |
将该对象与提供继承属性的另一个对象关联。传递 |
| [[IsExtensible]] | ( ) → Boolean | 确定是否允许向该对象添加更多属性。 |
| [[PreventExtensions]] | ( ) → Boolean |
控制是否可以向该对象添加新属性。返回 |
| [[GetOwnProperty]] |
(propertyKey) → Undefined | |
返回该对象自身属性的 |
| [[DefineOwnProperty]] | (propertyKey, 属性描述符) → Boolean |
创建或修改自身属性，其键为 propertyKey，具有 属性描述符 描述的状态。返回 |
| [[HasProperty]] | (propertyKey) → Boolean | 返回一个布尔值，指示该对象是否已经具有键为 propertyKey 的自身或继承属性。 |
| [[Get]] | (propertyKey, Receiver) → any |
从该对象返回键为 propertyKey 的属性的值。如果需要执行 ECMAScript 代码来检索属性值，Receiver 用作评估代码时的
|
| [[Set]] | (propertyKey, value, Receiver) → Boolean |
将键为 propertyKey 的属性的值设置为 value。如果需要执行 ECMAScript
代码来设置属性值，Receiver 用作评估代码时的 |
| [[Delete]] | (propertyKey) → Boolean |
从该对象中删除键为 propertyKey 的自身属性。如果属性未删除且仍存在，返回 |
| [[OwnPropertyKeys]] |
( ) → |
返回一个 |
| 内部方法 | 签名 | 描述 |
|---|---|---|
| [[Call]] |
(any, a |
执行与此对象关联的代码。通过函数调用表达式调用。内部方法的参数是一个 |
| [[Construct]] |
(a |
创建一个对象。通过 new 运算符或 super 调用调用。内部方法的第一个参数是一个 super
调用的参数。第二个参数是最初应用 new 运算符的对象。实现此内部方法的对象称为 |
普通对象和标准外来对象的基本内部方法的语义在第
6.1.7.3 基本内部方法的不变性
ECMAScript引擎中对象的内部方法必须符合下面指定的不变性列表。普通ECMAScript对象以及本规范中的所有标准
任何实现提供的
实现不得以任何方式允许绕过这些不变性，例如通过提供实现基本内部方法功能的替代接口而不强制执行其不变性。
定义:
- 内部方法的目标是调用内部方法的对象。
-
如果目标对象的[[IsExtensible]]内部方法返回
false ，或者其[[PreventExtensions]]内部方法返回true ，则该目标是不可扩展的。 - 不存在的属性是不可扩展目标对象上不存在的自有属性。
-
所有对
SameValue 的引用均根据SameValue 算法的定义。
返回值:
任何内部方法返回的值必须是一个
- [[Type]] =
normal ，[[Target]] =empty ，和[[Value]] = 该内部方法显示的“正常返回类型”的值，或 - [[Type]] =
throw ，[[Target]] =empty ，和[[Value]] = 任何ECMAScript语言值 。
[[GetPrototypeOf]] ( )
- 正常返回类型是Object或Null。
-
如果目标对象是不可扩展的，并且[[GetPrototypeOf]]返回一个值V，那么任何未来的[[GetPrototypeOf]]调用应返回与V相同的
SameValue 。
[[SetPrototypeOf]] ( V )
- 正常返回类型是Boolean。
-
如果目标对象是不可扩展的，[[SetPrototypeOf]]必须返回
false ，除非V与目标对象观察到的[[GetPrototypeOf]]值相同SameValue 。
[[IsExtensible]] ( )
- 正常返回类型是Boolean。
-
如果[[IsExtensible]]返回
false ，所有未来对该目标对象的[[IsExtensible]]调用必须返回false 。
[[PreventExtensions]] ( )
- 正常返回类型是Boolean。
-
如果[[PreventExtensions]]返回
true ，所有未来对该目标对象的[[IsExtensible]]调用必须返回false ，并且该目标对象现在被认为是不可扩展的。
[[GetOwnProperty]] ( P )
-
正常返回类型是
Property Descriptor 或Undefined。 -
如果返回值的类型是
Property Descriptor ，则返回值必须是一个完全填充的Property Descriptor 。 -
如果P被描述为不可配置、不可写的自有
数据属性 ，所有未来对[[GetOwnProperty]] ( P )的调用必须返回Property Descriptor ，其[[Value]]与P的[[Value]]属性相同SameValue 。 -
如果P的除了[[Writable]]和[[Value]]之外的属性可能会随时间变化，或者如果该属性可能会被删除，那么P的[[Configurable]]属性必须是
true 。 -
如果[[Writable]]属性可能从
false 变为true ，那么[[Configurable]]属性必须是true 。 -
如果目标对象是不可扩展的且P不存在，那么所有未来对该目标对象的[[GetOwnProperty]] ( P
)调用必须将P描述为不存在（即[[GetOwnProperty]] ( P
)必须返回
undefined ）。
由于第三个不变性的结果，如果一个属性被描述为
[[DefineOwnProperty]] ( P, Desc )
- 正常返回类型是Boolean。
-
[[DefineOwnProperty]]必须返回
false ，如果P之前已被观察为目标对象的不可配置自有属性，除非： -
[[DefineOwnProperty]] ( P, Desc )
必须返回
false ，如果目标对象是不可扩展的且P是一个不存在的自有属性。也就是说，一个不可扩展的目标对象不能被扩展新的属性。
[[HasProperty]] ( P )
- 正常返回类型是Boolean。
-
如果P之前已被观察为目标对象的不可配置自有数据或
访问器属性 ，[[HasProperty]]必须返回true 。
[[Get]] ( P, Receiver )
-
正常返回类型是任何
ECMAScript语言类型 。 -
如果P之前已被观察为目标对象的不可配置、不可写的自有
数据属性 ，其值为V，那么[[Get]]必须返回与V相同的SameValue 。 -
如果P之前已被观察为目标对象的不可配置自有
访问器属性 ，其[[Get]]属性为undefined ，[[Get]]操作必须返回undefined 。
[[Set]] ( P, V, Receiver )
- 正常返回类型是Boolean。
-
如果P之前已被观察为目标对象的不可配置、不可写的自有
数据属性 ，那么[[Set]]必须返回false ，除非V与P的[[Value]]属性相同SameValue 。 -
如果P之前已被观察为目标对象的不可配置自有
访问器属性 ，其[[Set]]属性为undefined ，[[Set]]操作必须返回false 。
[[Delete]] ( P )
- 正常返回类型是Boolean。
-
如果P之前已被观察为目标对象的不可配置自有数据或
访问器属性 ，[[Delete]]必须返回false 。
[[OwnPropertyKeys]] ( )
-
正常返回类型是
List 。 -
返回的
List 不得包含任何重复条目。 -
返回的
List 的每个元素的类型必须是String或Symbol。 -
返回的
List 必须至少包含所有之前观察到的不可配置自有属性的键。 -
如果目标对象是不可扩展的，返回的
List 必须仅包含目标对象的所有自有属性的键，这些属性可通过[[GetOwnProperty]]观察到。
[[Call]] ( )
-
正常返回类型是任何
ECMAScript语言类型 。
[[Construct]] ( )
- 正常返回类型是Object。
- 目标对象还必须具有[[Call]]内部方法。
6.1.7.4 众所周知的内在对象
众所周知的内在对象是内置对象，它们在本规范的算法中被明确引用，并且通常具有与
在本规范中，诸如%name%的引用意味着与当前
| 内置名称 | 全局名称 | ECMAScript 语言关联 |
|---|---|---|
|
|
AggregateError
|
AggregateError |
|
|
Array
|
Array |
|
|
ArrayBuffer
|
ArrayBuffer |
|
|
数组迭代器对象的原型 ( |
|
|
|
async-from-sync 迭代器对象的原型 ( |
|
|
|
异步函数对象的 |
|
|
|
异步迭代器对象的 |
|
|
|
所有标准内置异步迭代器对象间接继承的对象 | |
|
|
Atomics
|
Atomics 对象 ( |
|
|
BigInt
|
BigInt |
|
|
BigInt64Array
|
BigInt64Array |
|
|
BigUint64Array
|
BigUint64Array |
|
|
布尔值
|
布尔值 |
|
|
数据视图
|
数据视图 |
|
|
Date
|
Date |
|
|
decodeURI
|
decodeURI 函数 ( |
|
|
decodeURIComponent
|
decodeURIComponent 函数 ( |
|
|
encodeURI
|
encodeURI 函数 ( |
|
|
encodeURIComponent
|
encodeURIComponent 函数 ( |
|
|
Error
|
Error |
|
|
eval
|
eval 函数 ( |
|
|
EvalError
|
EvalError |
|
|
FinalizationRegistry
|
|
|
|
Float32Array
|
Float32Array |
|
|
Float64Array
|
Float64Array |
|
|
For-In 迭代器对象的原型 ( |
|
|
|
Function
|
Function |
|
|
生成器的构造函数 ( |
|
|
|
Int8Array
|
Int8Array |
|
|
Int16Array
|
Int16Array |
|
|
Int32Array
|
Int32Array |
|
|
isFinite
|
isFinite 函数 ( |
|
|
isNaN
|
isNaN 函数 ( |
|
|
所有标准内置迭代器对象间接继承的对象 | |
|
|
JSON
|
JSON 对象 ( |
|
|
Map
|
Map |
|
|
Map 迭代器对象的原型 ( |
|
|
|
Math
|
Math 对象 ( |
|
|
Number
|
Number |
|
|
Object
|
Object |
|
|
parseFloat
|
parseFloat 函数 ( |
|
|
parseInt
|
parseInt 函数 ( |
|
|
Promise
|
Promise |
|
|
Proxy
|
Proxy |
|
|
RangeError
|
RangeError |
|
|
ReferenceError
|
ReferenceError |
|
|
Reflect
|
Reflect 对象 ( |
|
|
RegExp
|
RegExp |
|
|
正则表达式字符串迭代器对象的原型 ( |
|
|
|
Set
|
Set |
|
|
Set 迭代器对象的原型 ( |
|
|
|
SharedArrayBuffer
|
SharedArrayBuffer |
|
|
String
|
String |
|
|
字符串迭代器对象的原型 ( |
|
|
|
Symbol
|
Symbol |
|
|
SyntaxError
|
SyntaxError |
|
|
一个 |
|
|
|
所有类型化数组 |
|
|
|
TypeError
|
TypeError |
|
|
Uint8Array
|
Uint8Array |
|
|
Uint8ClampedArray
|
Uint8ClampedArray |
|
|
Uint16Array
|
Uint16Array |
|
|
Uint32Array
|
Uint32Array |
|
|
URIError
|
URIError |
|
|
WeakMap
|
WeakMap |
|
|
WeakRef
|
|
|
|
WeakSet
|
WeakSet |
在
6.2 ECMAScript 规范类型
规范类型对应于在算法中使用的元值，用于描述 ECMAScript 语言结构和
6.2.1 枚举规范类型
枚举是规范内部的值，不能直接从 ECMAScript 代码中观察到。枚举用
6.2.2 列表和记录规范类型
列表类型用于解释参数列表的评估（参见 new 表达式、函数调用和其他需要简单有序值列表的算法中。列表类型的值是包含各个值的列表元素的简单有序序列。这些序列可以是任意长度的。列表元素可以使用基于 0
的索引随机访问。为了表示方便，可以使用类似数组的语法来访问列表元素。例如，arguments[2] 是表示列表 arguments 的第 3 个元素的简写。
当算法迭代列表元素而不指定顺序时，使用的顺序是列表中元素的顺序。
为了在本规范中表示方便，可以使用字面量语法来表示新的列表值。例如，« 1, 2 » 定义了一个包含两个元素的列表值，每个元素初始化为特定值。一个新的空列表可以表示为 « »。
在本规范中，短语“列表连接 A、B、...”（其中每个参数是一个可能为空的列表）表示一个新列表值，其元素是每个参数（按顺序）的元素（按顺序）的连接。
记录类型用于描述本规范算法中的数据聚合。记录类型值由一个或多个命名字段组成。每个字段的值是一个
为了在本规范中表示方便，可以使用类似对象字面量的语法来表示记录值。例如，{ [[Field1]]: 42, [[Field2]]:
在规范文本和算法中，可以使用点表示法来引用记录值的特定字段。例如，如果 R 是前一段中显示的记录，则 R.[[Field2]] 是“R 中名为 [[Field2]] 的字段”的简写。
常用记录字段组合的模式可以命名，并且该名称可以用作字面量记录值的前缀，以标识所描述的特定聚合类型。例如：PropertyDescriptor { [[Value]]:
42, [[Writable]]:
6.2.3 集合和关系规范类型
集合类型用于解释
关系类型用于解释对集合的约束。关系类型的值是其值域中值的有序对集合。例如，事件上的关系是事件的有序对集合。对于关系 R 和 R 值域中的两个值 a 和 b，a R b 是表示有序对 (a, b) 是 R 成员的简写。关系在某些条件下是最小的，当它是满足这些条件的最小关系时。
严格偏序是满足以下条件的关系值 R：
-
对于 R 域中的所有 a、b 和 c：
- 不是 a R a，并且
- 如果 a R b 和 b R c，则 a R c。
上述两个属性分别称为非自反性和传递性。
严格全序是满足以下条件的关系值 R：
-
对于 R 域中的所有 a、b 和 c：
- a 是 b 或 a R b 或 b R a，并且
- 不是 a R a，并且
- 如果 a R b 和 b R c，则 a R c。
上述三个属性分别称为完全性、非自反性和传递性。
6.2.4 完成记录规范类型
完成记录规范类型用于解释值和控制流的运行时传播，例如执行非本地控制转移的语句（break、continue、return
和 throw）的行为。
完成记录具有
以下简短术语有时用于指代完成记录。
- 正常完成指任何 [[Type]] 值为
normal 的完成记录。 - 中断完成指任何 [[Type]] 值为
break 的完成记录。 - 继续完成指任何 [[Type]] 值为
continue 的完成记录。 - 返回完成指任何 [[Type]] 值为
return 的完成记录。 - 抛出完成指任何 [[Type]] 值为
throw 的完成记录。 - 异常完成指任何 [[Type]] 值不是
normal 的完成记录。 - 某种类型的 正常完成包含 指 [[Value]] 字段中包含该类型值的正常完成。
本规范中定义的可调用对象仅返回正常完成或抛出完成。返回任何其他类型的完成记录被视为编辑错误。
6.2.4.1 NormalCompletion ( value )
抽象操作 NormalCompletion 接受参数 value（任何值，除了
- 返回
完成记录 { [[Type]]:normal , [[Value]]: value, [[Target]]:empty }.
6.2.4.2 ThrowCompletion ( value )
抽象操作 ThrowCompletion 接受参数 value（一个
- 返回
完成记录 { [[Type]]:throw , [[Value]]: value, [[Target]]:empty }.
6.2.4.3 UpdateEmpty ( completionRecord, value )
抽象操作 UpdateEmpty 接受参数 completionRecord（一个
6.2.5 引用记录规范类型
引用记录类型用于解释
delete、typeof、赋值运算符、super
引用记录是已解析的名称或属性绑定；其字段由
| 字段名称 | 值 | 含义 |
|---|---|---|
| [[Base]] | 一个 |
持有绑定的值或 |
| [[ReferencedName]] | 字符串、符号或 |
绑定的名称。如果 [[Base]] 值是 |
| [[Strict]] | 布尔值 | |
| [[ThisValue]] | 一个 |
如果不是 super |
以下
6.2.5.1 IsPropertyReference ( V )
抽象操作 IsPropertyReference 接受参数 V（一个
- 如果 V.[[Base]] 是
unresolvable ，返回false 。 - 如果 V.[[Base]] 是一个
环境记录 ，返回false ；否则返回true 。
6.2.5.2 IsUnresolvableReference ( V )
抽象操作 IsUnresolvableReference 接受参数 V（一个
- 如果 V.[[Base]] 是
unresolvable ，返回true ；否则返回false 。
6.2.5.3 IsSuperReference ( V )
抽象操作 IsSuperReference 接受参数 V（一个
- 如果 V.[[ThisValue]] 不是
empty ，返回true ；否则返回false 。
6.2.5.4 IsPrivateReference ( V )
抽象操作 IsPrivateReference 接受参数 V（一个
- 如果 V.[[ReferencedName]] 是
私有名称 ，返回true ；否则返回false 。
6.2.5.5 GetValue ( V )
抽象操作 GetValue 接受参数 V（一个
- 如果 V 不是一个
引用记录 ，返回 V。 - 如果
IsUnresolvableReference (V) 是true ，抛出一个ReferenceError 异常。 - 如果
IsPropertyReference (V) 是true ，那么- 令 baseObj 为
?
ToObject (V.[[Base]])。 - 如果
IsPrivateReference (V) 是true ，那么- 返回 ?
PrivateGet (baseObj, V.[[ReferencedName]])。
- 返回 ?
- 返回 ? baseObj.[[Get]](V.[[ReferencedName]],
GetThisValue (V))。
- 令 baseObj 为
?
- 否则，
6.2.5.6 PutValue ( V, W )
抽象操作 PutValue 接受参数 V（一个
- 如果 V 不是一个
引用记录 ，抛出一个ReferenceError 异常。 - 如果
IsUnresolvableReference (V) 是true ，那么- 如果 V.[[Strict]] 是
true ，抛出一个ReferenceError 异常。 - 令 globalObj 为
GetGlobalObject ()。 - 执行 ?
Set (globalObj, V.[[ReferencedName]], W,false )。 - 返回
unused 。
- 如果 V.[[Strict]] 是
- 如果
IsPropertyReference (V) 是true ，那么- 令 baseObj 为
?
ToObject (V.[[Base]])。 - 如果
IsPrivateReference (V) 是true ，那么- 返回 ?
PrivateSet (baseObj, V.[[ReferencedName]], W)。
- 返回 ?
- 令 succeeded 为 ? baseObj.[[Set]](V.[[ReferencedName]],
W,
GetThisValue (V))。 - 如果 succeeded 是
false 且 V.[[Strict]] 是true ，抛出一个TypeError 异常。 - 返回
unused 。
- 令 baseObj 为
?
- 否则，
6.2.5.7 GetThisValue ( V )
抽象操作GetThisValue接受参数V（一个
断言 ：IsPropertyReference (V) 是true 。- 如果
IsSuperReference (V) 是true ，返回V.[[ThisValue]]；否则返回V.[[Base]]。
6.2.5.8 InitializeReferencedBinding ( V, W )
抽象操作InitializeReferencedBinding接受参数V（一个
断言 ：IsUnresolvableReference (V) 是false 。- 设base为V.[[Base]]。
断言 ：base是一个环境记录 。- 返回 ? base.InitializeBinding(V.[[ReferencedName]], W)。
6.2.5.9 MakePrivateReference ( baseValue, privateIdentifier )
抽象操作MakePrivateReference接受参数baseValue（一个
- 设privEnv为
运行执行上下文 的PrivateEnvironment。 断言 ：privEnv不是null 。- 设privateName为
ResolvePrivateIdentifier (privEnv, privateIdentifier)。 - 返回
引用记录 { [[Base]]: baseValue, [[ReferencedName]]: privateName, [[Strict]]:true , [[ThisValue]]:empty }。
6.2.6 属性描述符规范类型
属性描述符类型用于解释对象属性属性的操作和具体化。属性描述符是一个
属性描述符值可以根据某些字段的存在或使用进一步分类为数据属性描述符和访问器属性描述符。数据属性描述符是包含名为[[Value]]或[[Writable]]的字段的描述符。访问器属性描述符是包含名为[[Get]]或[[Set]]的字段的描述符。任何属性描述符都可能包含名为[[Enumerable]]和[[Configurable]]的字段。属性描述符值不能同时是数据属性描述符和访问器属性描述符；然而，它可以既不是（在这种情况下，它是一个通用属性描述符）。一个完全填充的属性描述符是访问器属性描述符或数据属性描述符，并且具有
以下
6.2.6.1 IsAccessorDescriptor ( Desc )
抽象操作IsAccessorDescriptor接受参数Desc（一个
- 如果Desc是
undefined ，返回false 。 - 如果Desc有[[Get]]字段，返回
true 。 - 如果Desc有[[Set]]字段，返回
true 。 - 返回
false 。
6.2.6.2 IsDataDescriptor ( Desc )
抽象操作IsDataDescriptor接受参数Desc（一个
- 如果Desc是
undefined ，返回false 。 - 如果Desc有[[Value]]字段，返回
true 。 - 如果Desc有[[Writable]]字段，返回
true 。 - 返回
false 。
6.2.6.3 IsGenericDescriptor ( Desc )
抽象操作IsGenericDescriptor接受参数Desc（一个
- 如果Desc是
undefined ，返回false 。 - 如果
IsAccessorDescriptor (Desc) 是true ，返回false 。 - 如果
IsDataDescriptor (Desc) 是true ，返回false 。 - 返回
true 。
6.2.6.4 FromPropertyDescriptor ( Desc )
抽象操作FromPropertyDescriptor接受参数Desc（一个
- 如果Desc是
undefined ，返回undefined 。 - 设obj为
OrdinaryObjectCreate (%Object.prototype% )。 断言 ：obj是一个可扩展的普通对象 ，没有自己的属性。- 如果Desc有[[Value]]字段，则
- 执行!
CreateDataPropertyOrThrow (obj,"value" , Desc.[[Value]])。
- 执行!
- 如果Desc有[[Writable]]字段，则
- 执行!
CreateDataPropertyOrThrow (obj,"writable" , Desc.[[Writable]])。
- 执行!
- 如果Desc有[[Get]]字段，则
- 执行!
CreateDataPropertyOrThrow (obj,"get" , Desc.[[Get]])。
- 执行!
- 如果Desc有[[Set]]字段，则
- 执行!
CreateDataPropertyOrThrow (obj,"set" , Desc.[[Set]])。
- 执行!
- 如果Desc有[[Enumerable]]字段，则
- 执行!
CreateDataPropertyOrThrow (obj,"enumerable" , Desc.[[Enumerable]])。
- 执行!
- 如果Desc有[[Configurable]]字段，则
- 执行!
CreateDataPropertyOrThrow (obj,"configurable" , Desc.[[Configurable]])。
- 执行!
- 返回obj。
6.2.6.5 ToPropertyDescriptor ( Obj )
抽象操作ToPropertyDescriptor接受参数Obj（一个
- 如果Obj
不是一个对象 ，抛出一个TypeError 异常。 - 设desc为一个新
属性描述符 ，最初没有字段。 - 设hasEnumerable为?
HasProperty (Obj,"enumerable" )。 - 如果hasEnumerable是
true ，则 - 设hasConfigurable为?
HasProperty (Obj,"configurable" )。 - 如果hasConfigurable是
true ，则 - 设hasValue为?
HasProperty (Obj,"value" )。 - 如果hasValue是
true ，则- 设value为?
Get (Obj,"value" )。 - 设desc.[[Value]]为value。
- 设value为?
- 设hasWritable为?
HasProperty (Obj,"writable" )。 - 如果hasWritable是
true ，则 - 设hasGet为?
HasProperty (Obj,"get" )。 - 如果hasGet是
true ，则- 设getter为?
Get (Obj,"get" )。 - 如果
IsCallable (getter)是false 且getter不是undefined ，抛出一个TypeError 异常。 - 设desc.[[Get]]为getter。
- 设getter为?
- 设hasSet为?
HasProperty (Obj,"set" )。 - 如果hasSet是
true ，则- 设setter为?
Get (Obj,"set" )。 - 如果
IsCallable (setter)是false 且setter不是undefined ，抛出一个TypeError 异常。 - 设desc.[[Set]]为setter。
- 设setter为?
- 如果desc有[[Get]]字段或desc有[[Set]]字段，则
- 如果desc有[[Value]]字段或desc有[[Writable]]字段，抛出一个
TypeError 异常。
- 如果desc有[[Value]]字段或desc有[[Writable]]字段，抛出一个
- 返回desc。
6.2.6.6 CompletePropertyDescriptor ( Desc )
抽象操作CompletePropertyDescriptor接受参数Desc（一个
- 设like为
记录 { [[Value]]:undefined , [[Writable]]:false , [[Get]]:undefined , [[Set]]:undefined , [[Enumerable]]:false , [[Configurable]]:false }。 - 如果
IsGenericDescriptor (Desc) 是true 或IsDataDescriptor (Desc) 是true ，则- 如果Desc没有[[Value]]字段，设Desc.[[Value]]为like.[[Value]]。
- 如果Desc没有[[Writable]]字段，设Desc.[[Writable]]为like.[[Writable]]。
- 否则
- 如果Desc没有[[Get]]字段，设Desc.[[Get]]为like.[[Get]]。
- 如果Desc没有[[Set]]字段，设Desc.[[Set]]为like.[[Set]]。
- 如果Desc没有[[Enumerable]]字段，设Desc.[[Enumerable]]为like.[[Enumerable]]。
- 如果Desc没有[[Configurable]]字段，设Desc.[[Configurable]]为like.[[Configurable]]。
- 返回
未使用 。
6.2.7 环境记录规范类型
6.2.8 抽象闭包规范类型
抽象闭包规范类型用于引用算法步骤以及一组值。抽象闭包通过函数应用风格调用，例如closure(arg1, arg2)。与
在创建抽象闭包的算法步骤中，值通过“捕获”动词后跟别名列表来捕获。当创建抽象闭包时，它会捕获创建时与每个别名关联的值。在指定抽象闭包被调用时要执行的算法步骤中，每个捕获的值通过用于捕获该值的别名来引用。
如果抽象闭包返回一个
抽象闭包作为其他算法的一部分内联创建，如下例所示。
6.2.9 数据块
数据块规范类型用于描述一个独特且可变的字节大小（8位）数值序列。字节值是一个
为了在本规范中表示方便，可以使用类似数组的语法来访问数据块值的各个字节。这种表示法将数据块值呈现为从0开始的
驻留在可以被多个
共享数据块的语义通过
以下
6.2.9.1 CreateByteDataBlock ( size )
抽象操作CreateByteDataBlock接受参数size（一个非负
6.2.9.2 CreateSharedByteDataBlock ( size )
抽象操作 CreateSharedByteDataBlock 接受参数 size（一个非负的
- 令 db 为一个由 size 字节组成的新
共享数据块 值。如果无法创建这样的共享数据块 ，则抛出一个RangeError 异常。 - 令 execution 为
周围代理 的代理记录 的 [[CandidateExecution]] 字段。 - 令 eventsRecord 为 execution.[[EventsRecords]] 的
代理事件记录 ，其 [[AgentSignifier]] 为代理标识符 ()。 - 令 zero 为 « 0 »。
- 对于 db 的每个索引 i，执行以下步骤：
- 将
写共享内存 { [[Order]]:init , [[NoTear]]:true , [[Block]]: db, [[ByteIndex]]: i, [[ElementSize]]: 1, [[Payload]]: zero } 追加到 eventsRecord.[[EventList]]。
- 将
- 返回 db。
6.2.9.3 CopyDataBlockBytes ( toBlock, toIndex, fromBlock, fromIndex, count )
抽象操作 CopyDataBlockBytes 接受参数 toBlock（一个
断言 ：fromBlock 和 toBlock 是不同的值。- 令 fromSize 为 fromBlock 中的字节数。
断言 ：fromIndex + count ≤ fromSize。- 令 toSize 为 toBlock 中的字节数。
断言 ：toIndex + count ≤ toSize。- 重复，当 count > 0 时，执行以下步骤：
- 如果 fromBlock 是一个
共享数据块 ，则- 令 execution 为
周围代理 的代理记录 的 [[CandidateExecution]] 字段。 - 令 eventsRecord 为 execution.[[EventsRecords]] 的
代理事件记录 ，其 [[AgentSignifier]] 为代理标识符 ()。 - 令 bytes 为一个
列表 ，其唯一元素是一个不确定选择的字节值 。 - 注意：在实现中，bytes 是底层硬件上非原子读指令的结果。这种不确定性是
内存模型 的语义描述，用于描述具有弱一致性硬件的可观察行为。 - 令 readEvent 为
读共享内存 { [[Order]]:unordered , [[NoTear]]:true , [[Block]]: fromBlock, [[ByteIndex]]: fromIndex, [[ElementSize]]: 1 }。 - 将 readEvent 追加到 eventsRecord.[[EventList]]。
- 将
选择值记录 { [[Event]]: readEvent, [[ChosenValue]]: bytes } 追加到 execution.[[ChosenValues]]。 - 如果 toBlock 是一个
共享数据块 ，则- 将
写共享内存 { [[Order]]:unordered , [[NoTear]]:true , [[Block]]: toBlock, [[ByteIndex]]: toIndex, [[ElementSize]]: 1, [[Payload]]: bytes } 追加到 eventsRecord.[[EventList]]。
- 将
- 否则，
- 将 toBlock[toIndex] 设置为 bytes[0]。
- 令 execution 为
- 否则，
- 将 toIndex 设置为 toIndex + 1。
- 将 fromIndex 设置为 fromIndex + 1。
- 将 count 设置为 count - 1。
- 如果 fromBlock 是一个
- 返回
unused 。
6.2.10 私有元素规范类型
私有元素类型是一个
私有元素类型的值是
| 字段名称 | [[Kind]] 字段值 | 值 | 含义 |
|---|---|---|---|
| [[Key]] | 所有 |
一个 |
字段、方法或访问器的名称。 |
| [[Kind]] | 所有 |
|
元素的种类。 |
| [[Value]] |
|
一个 |
字段的值。 |
| [[Get]] |
|
一个 |
私有访问器的 getter。 |
| [[Set]] |
|
一个 |
私有访问器的 setter。 |
6.2.11 类字段定义记录规范类型
类字段定义类型是一个
类字段定义类型的值是
6.2.12 私有名称
私有名称规范类型用于描述一个全局唯一的值（不同于任何其他私有名称，即使它们在其他方面无法区分），该值表示私有类元素（字段、方法或访问器）的键。每个私有名称都有一个关联的不可变 [[Description]]，它是一个
6.2.13 类静态块定义记录规范类型
类静态块定义记录是一个
类静态块定义记录的字段列在
7 抽象操作
这些操作不是 ECMAScript 语言的一部分；它们在这里仅用于帮助规范 ECMAScript 语言的语义。其他更专业的
7.1 类型转换
ECMAScript 语言在需要时隐式执行自动类型转换。为了阐明某些结构的语义，定义了一组转换
ECMAScript 语言中的
7.1.1 ToPrimitive ( input [ , preferredType ] )
抽象操作 ToPrimitive 接受参数 input（一个
- 如果 input
是一个对象 ， then- 令 exoticToPrim 为 ?
GetMethod (input,@@toPrimitive )。 - 如果 exoticToPrim 不是
undefined ， then - 如果 preferredType 不存在，令
preferredType 为
number 。 - 返回 ?
OrdinaryToPrimitive (input, preferredType)。
- 令 exoticToPrim 为 ?
- 返回 input。
当 ToPrimitive 被调用时不带提示时，它的行为通常类似于提示为
7.1.1.1 OrdinaryToPrimitive ( O, hint )
抽象操作 OrdinaryToPrimitive 接受参数 O（一个对象）和 hint
（
- 如果 hint 是
string ，则- 令 methodNames 为 «
"toString" ,"valueOf" »。
- 令 methodNames 为 «
- 否则，
- 令 methodNames 为 «
"valueOf" ,"toString" »。
- 令 methodNames 为 «
- 对于 methodNames 的每个元素 name，执行
- 令 method 为 ?
Get (O, name)。 - 如果
IsCallable (method) istrue ，则
- 令 method 为 ?
- 抛出一个
TypeError 异常。
7.1.2 ToBoolean ( argument )
抽象操作 ToBoolean 接受参数 argument（一个
7.1.3 ToNumeric ( value )
抽象操作 ToNumeric 接受参数 value（一个
- 令 primValue 为 ?
ToPrimitive (value,number )。 - 如果 primValue
是一个 BigInt ，返回 primValue。 - 返回 ?
ToNumber (primValue)。
7.1.4 ToNumber ( argument )
抽象操作 ToNumber 接受参数 argument（一个
- 如果 argument
是一个数字 ，返回 argument。 - 如果 argument 是符号或 BigInt，抛出一个
TypeError 异常。 - 如果 argument 是
undefined ，返回NaN 。 - 如果 argument 是
null 或false ，返回+0 𝔽。 - 如果 argument 是
true ，返回1 𝔽。 - 如果 argument
是一个字符串 ，返回StringToNumber (argument)。 断言 ：argument是一个对象 。- 令 primValue 为 ?
ToPrimitive (argument,number )。 断言 ：primValue不是一个对象 。- 返回 ?
ToNumber (primValue)。
7.1.4.1 ToNumber 应用于字符串类型
抽象操作
语法
所有未明确定义的语法符号均使用词法语法中为数字字面量定义的定义（
7.1.4.1.1 StringToNumber ( str )
抽象操作 StringToNumber 接受参数 str（一个字符串）并返回一个数字。 当调用时，它执行以下步骤：
- 令 text 为
StringToCodePoints (str). - 令 literal 为
ParseText (text,StringNumericLiteral ). - 如果 literal 是一个
List 的错误，返回NaN . - 返回
StringNumericValue 的 literal.
7.1.4.1.2 运行时语义：StringNumericValue
语法导向操作
将
它在以下产生式上分段定义：
- 返回
+0 𝔽。
- 返回
𝔽 (MV ofNonDecimalIntegerLiteral )。
- 令 a 为
StringNumericValue 的StrUnsignedDecimalLiteral 。 - 如果 a 是
+0 𝔽，返回-0 𝔽。 - 返回 -a。
- 返回
+∞ 𝔽。
- 令 a 为第一个
DecimalDigits 的 MV。 - 如果第二个
DecimalDigits 存在，则- 令 b 为第二个
DecimalDigits 的 MV。 - 令 n 为第二个
DecimalDigits 的代码点数。
- 令 b 为第二个
- 否则，
- 令 b 为 0。
- 令 n 为 0。
- 如果
ExponentPart 存在，令 e 为ExponentPart 的 MV。否则，令 e 为 0。 - 返回
RoundMVResult ((a + (b × 10-n)) × 10e)。
- 令 b 为
DecimalDigits 的 MV。 - 如果
ExponentPart 存在，令 e 为ExponentPart 的 MV。否则，令 e 为 0。 - 令 n 为
DecimalDigits 的代码点数。 - 返回
RoundMVResult (b × 10e - n)。
- 令 a 为
DecimalDigits 的 MV。 - 如果
ExponentPart 存在，令 e 为ExponentPart 的 MV。否则，令 e 为 0。 - 返回
RoundMVResult (a × 10e)。
7.1.4.1.3 RoundMVResult ( n )
抽象操作 RoundMVResult 接受参数 n（一个
- 如果 n 的十进制表示有 20 个或更少的有效数字，返回
𝔽 (n)。 - 令 option1 为结果的
mathematical value ，其中 n 的十进制表示中第 20 位之后的每个有效数字都被替换为 0。 - 令 option2 为结果的
mathematical value ，其中 n 的十进制表示中第 20 位之后的每个有效数字都被替换为 0，然后在第 20 位处递增（必要时进位）。 - 令 chosen 为
实现定义 的 option1 或 option2 的选择。 - 返回
𝔽 (chosen)。
7.1.5 ToIntegerOrInfinity ( argument )
抽象操作 ToIntegerOrInfinity 接受参数 argument（一个
7.1.6 ToInt32 ( argument )
抽象操作 ToInt32 接受参数 argument（一个
根据上述 ToInt32 的定义：
- ToInt32 抽象操作是幂等的：如果应用于其产生的结果，第二次应用不会改变该值。
-
ToInt32(
ToUint32 (x)) 与 ToInt32(x) 对于所有 x 的值是相同的。（为了保持这一特性，+∞ 𝔽 和-∞ 𝔽 被映射到+0 𝔽。） -
ToInt32 将
-0 𝔽 映射到+0 𝔽。
7.1.7 ToUint32 ( argument )
抽象操作 ToUint32 接受参数 argument（一个
7.1.8 ToInt16 ( argument )
抽象操作 ToInt16 接受参数 argument（一个
7.1.9 ToUint16 ( argument )
抽象操作 ToUint16 接受参数 argument（一个
根据上述 ToUint16 的定义：
-
在第
4 步中将 216 替换为 232 是 ToUint32 和 ToUint16 唯一的区别。 -
ToUint16 将
-0 𝔽 映射为+0 𝔽。
7.1.10 ToInt8 ( argument )
抽象操作 ToInt8 接受参数 argument（一个
7.1.11 ToUint8（argument）
抽象操作ToUint8接受参数argument（一个ECMAScript语言值），并返回一个包含整数Number的正常完成或一个抛出完成。它将argument转换为从
7.1.12 ToUint8Clamp ( argument )
抽象操作 ToUint8Clamp 接受参数 argument（一个
与大多数其他 ECMAScript Math.round
7.1.13 ToBigInt ( argument )
抽象操作 ToBigInt 接受参数 argument（一个
- 令 prim 为 ?
ToPrimitive (argument,number )。 - 返回 prim 在
表 12 中对应的值。
| 参数类型 | 结果 |
|---|---|
| Undefined | 抛出 |
| Null | 抛出 |
| Boolean | 如果 prim 是 1n；如果 prim 是
0n。
|
| BigInt | 返回 prim。 |
| Number | 抛出 |
| String |
|
| Symbol | 抛出 |
7.1.14 StringToBigInt ( str )
抽象操作 StringToBigInt 接受参数 str（一个字符串）并返回一个 BigInt 或
- 令 text 为
StringToCodePoints (str)。 - 令 literal 为
ParseText (text,StringIntegerLiteral )。 - 如果 literal 是一个
错误列表 ，返回undefined 。 - 令 mv 为 literal 的 MV。
断言 ：mv 是一个整数 。- 返回
ℤ (mv)。
7.1.14.1 StringIntegerLiteral 语法
语法
7.1.14.2 运行时语义：MV
-
StringIntegerLiteral ::: StrWhiteSpace opt -
StringIntegerLiteral ::: StrWhiteSpace opt StrIntegerLiteral StrWhiteSpace opt StrIntegerLiteral 的 MV。
7.1.15 ToBigInt64 ( argument )
抽象操作 ToBigInt64 接受参数 argument（一个
7.1.16 ToBigUint64 ( argument )
抽象操作 ToBigUint64 接受参数 argument（一个
7.1.17 ToString ( argument )
抽象操作 ToString 接受参数 argument（一个
- 如果 argument
是一个字符串 ，返回 argument。 - 如果 argument
是一个符号 ，抛出一个TypeError 异常。 - 如果 argument 是
undefined ，返回"undefined" 。 - 如果 argument 是
null ，返回"null" 。 - 如果 argument 是
true ，返回"true" 。 - 如果 argument 是
false ，返回"false" 。 - 如果 argument
是一个数字 ，返回Number::toString (argument, 10)。 - 如果 argument
是一个 BigInt ，返回BigInt::toString (argument, 10)。 断言 ：argument是一个对象 。- 令 primValue 为 ?
ToPrimitive (argument,string )。 断言 ：primValue不是一个对象 。- 返回 ?
ToString (primValue)。
7.1.18 ToObject ( argument )
抽象操作 ToObject 接受参数 argument（一个
| 参数类型 | 结果 |
|---|---|
| Undefined | 抛出一个 |
| Null | 抛出一个 |
| Boolean | 返回一个新的布尔对象，其 [[BooleanData]] 内部槽被设置为 argument。参见 |
| Number | 返回一个新的数字对象，其 [[NumberData]] 内部槽被设置为 argument。参见 |
| String | 返回一个新的字符串对象，其 [[StringData]] 内部槽被设置为 argument。参见 |
| Symbol | 返回一个新的符号对象，其 [[SymbolData]] 内部槽被设置为 argument。参见 |
| BigInt | 返回一个新的 BigInt 对象，其 [[BigIntData]] 内部槽被设置为 argument。参见
|
| Object | 返回 argument。 |
7.1.19 ToPropertyKey ( argument )
抽象操作 ToPropertyKey 接受参数 argument（一个
- 令 key 为 ?
ToPrimitive (argument,string )。 - 如果 key
是一个符号 ，那么- 返回 key。
- 返回 !
ToString (key)。
7.1.20 ToLength ( argument )
抽象操作 ToLength 接受参数 argument（一个
- 令 len 为 ?
ToIntegerOrInfinity (argument)。 - 如果 len ≤ 0，返回
+0 𝔽。 - 返回
𝔽 (min (len, 253 - 1))。
7.1.21 CanonicalNumericIndexString ( argument )
抽象操作 CanonicalNumericIndexString 接受参数 argument（一个字符串）并返回一个数字或
一个规范数字字符串是任何使 CanonicalNumericIndexString
抽象操作不返回
7.1.22 ToIndex ( value )
抽象操作 ToIndex 接受参数 value（一个
- 令 integer 为 ?
ToIntegerOrInfinity (value)。 - 如果 integer 不在从 0 到 253 - 1 的
闭区间 内，抛出一个RangeError 异常。 - 返回 integer。
7.2 测试和比较操作
7.2.1 RequireObjectCoercible ( argument )
抽象操作 RequireObjectCoercible 接受参数 argument（一个
| 参数类型 | 结果 |
|---|---|
| Undefined | 抛出一个 |
| Null | 抛出一个 |
| Boolean | 返回 argument。 |
| Number | 返回 argument。 |
| String | 返回 argument。 |
| Symbol | 返回 argument。 |
| BigInt | 返回 argument。 |
| Object | 返回 argument。 |
7.2.2 IsArray ( argument )
抽象操作 IsArray 接受参数 argument（一个
- 如果 argument
不是一个对象 ，返回false 。 - 如果 argument 是一个
数组异质对象 ，返回true 。 - 如果 argument 是一个
代理异质对象 ，那么- 执行 ?
ValidateNonRevokedProxy (argument)。 - 令 proxyTarget 为 argument.[[ProxyTarget]]。
- 返回 ?
IsArray (proxyTarget)。
- 执行 ?
- 返回
false 。
7.2.3 IsCallable ( argument )
抽象操作 IsCallable 接受参数 argument（一个
- 如果 argument
不是一个对象 ，返回false 。 - 如果 argument 具有 [[Call]] 内部方法，返回
true 。 - 返回
false 。
7.2.4 IsConstructor ( argument )
抽象操作 IsConstructor 接受参数 argument（一个
- 如果 argument
不是一个对象 ，返回false 。 - 如果 argument 具有 [[Construct]]
内部方法，返回
true 。 - 返回
false 。
7.2.5 IsExtensible ( O )
抽象操作 IsExtensible 接受参数 O（一个对象），并返回一个
- 返回 ? O.[[IsExtensible]]()。
7.2.6 IsIntegralNumber ( argument )
抽象操作 IsIntegralNumber 接受参数 argument（一个
7.2.7 IsPropertyKey ( argument )
抽象操作 IsPropertyKey 接受参数 argument（一个
7.2.8 IsRegExp ( argument )
抽象操作 IsRegExp 接受参数 argument（一个
7.2.9 静态语义：IsStringWellFormedUnicode ( string )
抽象操作 IsStringWellFormedUnicode 接受参数 string（一个字符串），并返回一个布尔值。它将 string 解释为一系列 UTF-16
编码的代码点，如
- 令 len 为 string 的长度。
- 令 k 为 0。
- 重复，直到 k < len，
- 令 cp 为
CodePointAt (string, k)。 - 如果 cp.[[IsUnpairedSurrogate]] 为
true ，返回false 。 - 将 k 设置为 k + cp.[[CodeUnitCount]]。
- 令 cp 为
- 返回
true 。
7.2.10 SameValue ( x, y )
抽象操作 SameValue 接受参数 x（一个
- 如果
Type (x) 不是Type (y)，返回false 。 - 如果 x
是一个数字 ，那么- 返回
Number::sameValue (x, y)。
- 返回
- 返回
SameValueNonNumber (x, y)。
这个算法不同于
7.2.11 SameValueZero ( x, y )
抽象操作 SameValueZero 接受参数 x（一个
- 如果
Type (x) 不是Type (y)，返回false 。 - 如果 x
是一个数字 ，那么- 返回
Number::sameValueZero (x, y)。
- 返回
- 返回
SameValueNonNumber (x, y)。
SameValueZero 与
7.2.12 SameValueNonNumber ( x, y )
抽象操作 SameValueNonNumber 接受参数 x（一个
断言 ：Type (x) 是Type (y)。- 如果 x 是
null 或undefined ，返回true 。 - 如果 x
是一个 BigInt ，那么- 返回
BigInt::equal (x, y)。
- 返回
- 如果 x
是一个字符串 ，那么- 如果 x 和 y 具有相同的长度并且在相同的位置具有相同的代码单元，返回
true ；否则，返回false 。
- 如果 x 和 y 具有相同的长度并且在相同的位置具有相同的代码单元，返回
- 如果 x
是一个布尔值 ，那么- 如果 x 和 y 都是
true 或都为false ，返回true ；否则，返回false 。
- 如果 x 和 y 都是
- 注意：所有其他
ECMAScript 语言值 通过身份进行比较。 - 如果 x 是 y，返回
true ；否则，返回false 。
7.2.13 IsLessThan ( x, y, LeftFirst )
抽象操作 IsLessThan 接受参数 x（一个
- 如果 LeftFirst 是
true ，则- 令 px 为 ?
ToPrimitive (x,number ). - 令 py 为 ?
ToPrimitive (y,number ).
- 令 px 为 ?
- 否则
- 注意：需要反转求值顺序以保持从左到右的求值。
- 令 py 为 ?
ToPrimitive (y,number ). - 令 px 为 ?
ToPrimitive (x,number ).
- 如果 px
是一个 字符串 且 py是一个 字符串 ，则 - 否则
- 如果 px
是一个 BigInt 且 py是一个 字符串 ，则- 令 ny 为
StringToBigInt (py). - 如果 ny 是
undefined ，返回undefined . - 返回
BigInt::lessThan (px, ny).
- 令 ny 为
- 如果 px
是一个 字符串 且 py是一个 BigInt ，则- 令 nx 为
StringToBigInt (px). - 如果 nx 是
undefined ，返回undefined . - 返回
BigInt::lessThan (nx, py).
- 令 nx 为
- 注意：因为 px 和 py 是原始值，求值顺序不重要。
- 令 nx 为 ?
ToNumeric (px). - 令 ny 为 ?
ToNumeric (py). - 如果
Type (nx) 是Type (ny)，则- 如果 nx
是一个 数字 ，则- 返回
Number::lessThan (nx, ny).
- 返回
- 否则
断言 ：nx是一个 BigInt .- 返回
BigInt::lessThan (nx, ny).
- 如果 nx
断言 ：nx是一个 BigInt 且 ny是一个 数字 ，或 nx是一个 数字 且 ny是一个 BigInt .- 如果 nx 或 ny 是
NaN ， 返回undefined . - 如果 nx 是
-∞ 𝔽 或 ny 是+∞ 𝔽，返回true . - 如果 nx 是
+∞ 𝔽 或 ny 是-∞ 𝔽，返回false . - 如果
ℝ (nx) <ℝ (ny)，返回true ；否则返回false .
- 如果 px
字符串的比较使用简单的按 UTF-16 代码单元值序列的字典顺序，没有尝试使用 Unicode 规范中定义的更复杂的、语义导向的字符或字符串相等性和排序顺序定义。因此，根据 Unicode
标准正规等价但不在相同规范化形式中的字符串值可能会被测试为不等。同样需要注意的是，对于包含
7.2.14 IsLooselyEqual ( x, y )
抽象操作 IsLooselyEqual 接受参数 x（一个 == 操作符的语义。它在被调用时执行以下步骤：
- 如果
类型 (x) 和类型 (y) 相同，则- 返回
严格相等 (x, y)。
- 返回
- 如果 x 是
null 且 y 是undefined ，返回true 。 - 如果 x 是
undefined 且 y 是null ，返回true 。 - 注意：这一步在章节
B.3.6.2 中被替换。 - 如果 x
是数字 且 y是字符串 ，返回 !宽松相等 (x, !转换为数字 (y))。 - 如果 x
是字符串 且 y是数字 ，返回 !宽松相等 (!转换为数字 (x), y)。 - 如果 x
是 BigInt 且 y是字符串 ，则- 令 n 为
字符串转换为 BigInt (y)。 - 如果 n 是
undefined ，返回false 。 - 返回 !
宽松相等 (x, n)。
- 令 n 为
- 如果 x
是字符串 且 y是 BigInt ，返回 !宽松相等 (y, x)。 - 如果 x
是布尔值 ，返回 !宽松相等 (!转换为数字 (x), y)。 - 如果 y
是布尔值 ，返回 !宽松相等 (x, !转换为数字 (y))。 - 如果 x 是字符串、数字、BigInt 或 Symbol 且 y
是对象 ，返回 !宽松相等 (x, ?转换为原始值 (y))。 - 如果 x
是对象 且 y 是字符串、数字、BigInt 或 Symbol，返回 !宽松相等 (?转换为原始值 (x), y)。 - 如果 x
是 BigInt 且 y是数字 ，或如果 x是数字 且 y是 BigInt ，则 - 返回
false 。
7.2.15 IsStrictlyEqual ( x, y )
抽象操作 IsStrictlyEqual 接受参数 x（一个 === 操作符的语义。调用时执行以下步骤：
-
如果
Type (x) 不是Type (y)，返回false 。 -
如果 x
是一个数字 ，则-
返回
Number::equal (x, y)。
-
返回
-
返回
SameValueNonNumber (x, y)。
该算法在处理有符号零和 NaN 时与
7.3 对象操作
7.3.1 MakeBasicObject ( internalSlotsList )
抽象操作 MakeBasicObject 接受参数 internalSlotsList（一个
- 让 obj 成为一个新创建的对象，其内部包含 internalSlotsList 中每个名称的内部插槽。
- 将 obj 的关键内部方法设置为默认的
普通对象 定义，详见10.1 。 Assert ：如果调用者不会覆盖 obj 的 [[GetPrototypeOf]] 和 [[SetPrototypeOf]] 关键内部方法中的任意一个，则 internalSlotsList 包含 [[Prototype]]。Assert ：如果调用者不会覆盖 obj 的 [[SetPrototypeOf]]、[[IsExtensible]] 和 [[PreventExtensions]] 关键内部方法中的所有一个或多个，则 internalSlotsList 包含 [[Extensible]]。- 如果 internalSlotsList 包含 [[Extensible]]，则将 obj.[[Extensible]] 设置为
true 。 - 返回 obj。
在本规范中，
7.3.2 Get ( O, P )
抽象操作 Get 接受参数 O（一个对象）和 P（一个
- 返回 ? O.[[Get]](P, O).
7.3.3 GetV ( V, P )
抽象操作 GetV 接受参数 V（一个
- 让 O 成为 ?
ToObject (V). - 返回 ? O.[[Get]](P, V).
7.3.4 Set ( O, P, V, Throw )
抽象操作 Set 接受参数 O（一个对象）、P（一个
- 让 success 成为 ? O.[[Set]](P, V, O).
- 如果 success 是
false 并且 Throw 是true ，则抛出一个TypeError 异常。 - 返回
unused .
7.3.5 CreateDataProperty ( O, P, V )
抽象操作 CreateDataProperty 接受参数 O（一个对象）、P（一个
- 让 newDesc 成为属性描述符 { [[Value]]:
V, [[Writable]]:
true , [[Enumerable]]:true , [[Configurable]]:true }. - 返回 ? O.[[DefineOwnProperty]](P, newDesc).
此抽象操作创建一个属性，其属性设置为 ECMAScript 语言赋值运算符创建的默认值。通常，该属性不会已存在。如果存在且不可配置，或者 O 不可扩展，则 [[DefineOwnProperty]] 将返回
7.3.6 CreateDataPropertyOrThrow ( O, P, V )
抽象操作 CreateDataPropertyOrThrow 接受参数 O（一个对象）、P（一个
- 让 success 成为 ?
CreateDataProperty (O, P, V). - 如果 success 是
false ，则抛出一个TypeError 异常。 - 返回
unused .
此抽象操作创建一个属性，其属性设置为 ECMAScript 语言赋值运算符创建的默认值。通常，该属性不会已存在。如果存在且不可配置，或者 O 不可扩展，则 [[DefineOwnProperty]] 将返回
7.3.7 CreateNonEnumerableDataPropertyOrThrow ( O, P, V )
抽象操作 CreateNonEnumerableDataPropertyOrThrow 接受参数 O（一个对象）、P（一个
Assert : O 是一个普通的、可扩展的对象，并且没有不可配置的属性。- 让 newDesc 成为属性描述符 { [[Value]]:
V, [[Writable]]:
true , [[Enumerable]]:false , [[Configurable]]:true }. - 执行 !
DefinePropertyOrThrow (O, P, newDesc). - 返回
unused .
此抽象操作创建一个属性，其属性设置为与 ECMAScript 语言赋值运算符创建的默认值相同，但不可枚举。通常情况下，该属性不存在。如果存在，则
7.3.8 DefinePropertyOrThrow ( O, P, desc )
抽象操作 DefinePropertyOrThrow 接受参数 O（一个对象）、P（一个
- 让 success 成为 ? O.[[DefineOwnProperty]](P, desc).
- 如果 success 是
false ，则抛出TypeError 异常。 - 返回
unused .
7.3.9 DeletePropertyOrThrow ( O, P )
抽象操作 DeletePropertyOrThrow 接受参数 O（一个对象）和 P（一个
- 让 success 成为 ? O.[[Delete]](P).
- 如果 success 是
false ，则抛出TypeError 异常。 - 返回
unused .
7.3.10 GetMethod ( V, P )
抽象操作 GetMethod 接受参数 V（一个
- 让 func 成为 ?
GetV (V, P). - 如果 func 是
undefined 或null ，则返回undefined 。 - 如果
IsCallable (func) 是false ，则抛出TypeError 异常。 - 返回 func。
7.3.11 HasProperty ( O, P )
抽象操作 HasProperty 接受参数 O（一个 Object）和 P（一个
- 返回 ? O.[[HasProperty]](P)。
7.3.12 HasOwnProperty ( O, P )
抽象操作 HasOwnProperty 接受参数 O（一个 Object）和 P（一个
- Let desc be ? O.[[GetOwnProperty]](P).
- If desc is
undefined , returnfalse . - Return
true .
7.3.13 Call ( F, V [ , argumentsList ] )
抽象操作 Call 接受参数 F（一个
- 如果argumentsList不存在，则将argumentsList设为一个新的空
List 。 - 如果
IsCallable (F)的返回值为false ，则抛出TypeError 异常。 - 返回 ? F.[[Call]](V, argumentsList)。
7.3.14 构造（F [ , argumentsList [ , newTarget ] ]）
抽象操作构造（Construct）接受参数F（一个
- 如果newTarget不存在，则将newTarget设为F。
- 如果argumentsList不存在，则将argumentsList设为一个新的空
List 。 - 返回 ? F.[[Construct]](argumentsList, newTarget)。
如果newTarget不存在，则该操作等效于：new F(...argumentsList)
7.3.15 SetIntegrityLevel ( O, level )
抽象操作 SetIntegrityLevel 接受参数 O（一个对象）和 level（
- 设 status 为 ? O.[[PreventExtensions]]()。
- 如果 status 是
false ，则返回false 。 - 设 keys 为 ? O.[[OwnPropertyKeys]]()。
- 如果 level 是
sealed ，则- 对于 keys 的每个元素 k，执行
- 执行 ?
DefinePropertyOrThrow (O, k, PropertyDescriptor { [[Configurable]]:false })。
- 执行 ?
- 对于 keys 的每个元素 k，执行
- 否则，
Assert ： level 是frozen 。- 对于 keys 的每个元素 k，执行
- 设 currentDesc 为 ? O.[[GetOwnProperty]](k)。
- 如果 currentDesc 不是
undefined ，则- 如果
IsAccessorDescriptor (currentDesc) 是true ，则- 设 desc 为 PropertyDescriptor { [[Configurable]]:
false }。
- 设 desc 为 PropertyDescriptor { [[Configurable]]:
- 否则，
- 设 desc 为 PropertyDescriptor { [[Configurable]]:
false , [[Writable]]:false }。
- 设 desc 为 PropertyDescriptor { [[Configurable]]:
- 执行 ?
DefinePropertyOrThrow (O, k, desc)。
- 如果
- 返回
true 。
7.3.16 TestIntegrityLevel ( O, level )
抽象操作 TestIntegrityLevel 接受参数 O（一个对象）和 level（
- 设 extensible 为 ?
IsExtensible (O)。 - 如果 extensible 是
true ，则返回false 。 - 注意：如果对象是可扩展的，则不检查其任何属性。
- 设 keys 为 ? O.[[OwnPropertyKeys]]()。
- 对于 keys 的每个元素 k，执行
- 设 currentDesc 为 ? O.[[GetOwnProperty]](k)。
- 如果 currentDesc 不是
undefined ，则- 如果 currentDesc.[[Configurable]] 是
true ，则返回false 。 - 如果 level 是
frozen 并且IsDataDescriptor (currentDesc) 是true ，则- 如果 currentDesc.[[Writable]] 是
true ，则返回false 。
- 如果 currentDesc.[[Writable]] 是
- 如果 currentDesc.[[Configurable]] 是
- 返回
true 。
7.3.17 CreateArrayFromList ( elements )
抽象操作 CreateArrayFromList 接受参数 elements（一个
- 设 array 为 !
ArrayCreate (0)。 - 设 n 为 0。
- 对于 elements 的每个元素 e，执行
- 执行 !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (n)), e)。 - 将 n 设为 n + 1。
- 执行 !
- 返回 array。
7.3.18 LengthOfArrayLike ( obj )
抽象操作 LengthOfArrayLike 接受参数 obj（一个对象）并返回一个
类似数组对象是指该操作返回
7.3.19 CreateListFromArrayLike ( obj [ , elementTypes ] )
抽象操作 CreateListFromArrayLike 接受参数 obj（一个
- 如果 elementTypes 不存在，则将 elementTypes 设置为« Undefined, Null, Boolean, String, Symbol, Number, BigInt, Object »。
- 如果 obj
不是对象 ，则抛出TypeError 异常。 - 让 len 是 ?
LengthOfArrayLike (obj)。 - 让 list 是一个新的空
List 。 - 让 index 是 0。
- 重复，当 index < len 时，
- 返回 list。
7.3.20 Invoke ( V, P [ , argumentsList ] )
抽象操作 Invoke 接受参数 V（一个
7.3.21 OrdinaryHasInstance ( C, O )
抽象操作 OrdinaryHasInstance 接受参数 C（一个
- 如果
IsCallable (C) 为false ，返回false 。 - 如果 C 有一个 [[BoundTargetFunction]] 内部插槽，则
- 让 BC 为 C.[[BoundTargetFunction]]。
- 返回 ?
InstanceofOperator (O, BC)。
- 如果 O
不是一个对象 ，返回false 。 - 让 P 为 ?
Get (C,"prototype" )。 - 如果 P
不是一个对象 ，抛出一个TypeError 异常。 - 重复，
- 将 O 设置为 ? O.[[GetPrototypeOf]]()。
- 如果 O 是
null ，返回false 。 - 如果
SameValue (P, O) 是true ，返回true 。
7.3.22 SpeciesConstructor ( O, defaultConstructor )
抽象操作 SpeciesConstructor 接受参数 O（一个对象）和 defaultConstructor（一个
- 让 C 为 ?
Get (O,"constructor" )。 - 如果 C 是
undefined ，返回 defaultConstructor。 - 如果 C
不是一个对象 ，抛出一个TypeError 异常。 - 让 S 为 ?
Get (C,@@species )。 - 如果 S 是
undefined 或者null ，返回 defaultConstructor。 - 如果
IsConstructor (S) 是true ，返回 S。 - 抛出一个
TypeError 异常。
7.3.23 EnumerableOwnProperties ( O, kind )
抽象操作 EnumerableOwnProperties 接受参数 O（一个对象）和 kind
（
- 让 ownKeys 为 ? O.[[OwnPropertyKeys]]()。
- 让 results 为一个新的空
列表 。 - 对于 ownKeys 的每个元素 key，做如下操作：
- 如果 key 是
字符串 ，那么：- 让 desc 为 ? O.[[GetOwnProperty]](key)。
- 如果 desc 不是
undefined 并且 desc.[[Enumerable]] 是true ，那么：- 如果 kind 是
key ，那么- 将 key 添加到 results 中。
- 否则，
- 让 value 为 ?
Get (O, key)。 - 如果 kind 是
value ，那么：- 将 value 添加到 results 中。
- 否则，
断言 ：kind 是key+value 。- 让 entry 为
CreateArrayFromList (« key, value »)。 - 将 entry 添加到 results 中。
- 让 value 为 ?
- 如果 kind 是
- 如果 key 是
- 返回 results。
7.3.24 GetFunctionRealm ( obj )
抽象操作 GetFunctionRealm 接受参数 obj（一个
- 如果 obj 拥有一个 [[Realm]] 内部插槽，则：
- 返回 obj.[[Realm]]。
- 如果 obj 是一个
绑定函数的外来对象 ，则：- 让 boundTargetFunction 为 obj.[[BoundTargetFunction]]。
- 返回 ?
GetFunctionRealm (boundTargetFunction)。
- 如果 obj 是一个
代理的外来对象 ，则：- 执行 ?
ValidateNonRevokedProxy (obj)。 - 让 proxyTarget 为 obj.[[ProxyTarget]]。
- 返回 ?
GetFunctionRealm (proxyTarget)。
- 执行 ?
- 返回
当前域记录 。
7.3.25 CopyDataProperties ( target, source, excludedItems )
抽象操作 CopyDataProperties 接受参数 target（一个对象），source
（一个
- 如果 source 是
undefined 或null ，则返回unused 。 - 让 from 为 !
ToObject (source)。 - 让 keys 为 ? from.[[OwnPropertyKeys]]()。
- 对于 keys 中的每个元素 nextKey，执行以下步骤：
- 让 excluded 为
false 。 - 对于 excludedItems 中的每个元素 e，执行以下步骤：
- 如果
SameValue (e, nextKey) 是true ，则执行以下步骤：- 将 excluded 设为
true 。
- 将 excluded 设为
- 如果
- 如果 excluded 是
false ，则执行以下步骤：- 让 desc 为 ? from.[[GetOwnProperty]](nextKey)。
- 如果 desc 不是
undefined 并且 desc.[[Enumerable]] 是true ，则执行以下步骤：- 让 propValue 为 ?
Get (from, nextKey)。 - 执行 !
CreateDataPropertyOrThrow (target, nextKey, propValue)。
- 让 propValue 为 ?
- 让 excluded 为
- 返回
unused 。
这里传入的目标对象始终是一个新创建的对象，在发生错误抛出时不会直接访问到它。
7.3.26 PrivateElementFind ( O, P )
抽象操作 PrivateElementFind 接受参数 O（一个对象）和 P（一个
- 如果 O.[[PrivateElements]]
包含一个
PrivateElement pe， 使得 pe.[[Key]] 是 P，则执行以下步骤：- 返回 pe。
- 返回
empty 。
7.3.27 PrivateFieldAdd ( O, P, value )
抽象操作 PrivateFieldAdd 接受参数 O（一个对象），P（一个
- If the
host is a web browser, then- 执行 ?
HostEnsureCanAddPrivateElement (O).
- 执行 ?
- Let entry be
PrivateElementFind (O, P). - If entry is not
empty , throw aTypeError exception. - Append
PrivateElement { [[Key]]: P, [[Kind]]:field , [[Value]]: value } to O.[[PrivateElements]]. - Return
unused .
7.3.28 PrivateMethodOrAccessorAdd ( O, method )
抽象操作 PrivateMethodOrAccessorAdd 接受参数 O（一个对象）和 method（一个
Assert : method.[[Kind]] 是method 或accessor 。- 如果
主机环境 是 Web 浏览器，则执行：- 执行 ?
HostEnsureCanAddPrivateElement (O)。
- 执行 ?
- 让 entry 成为
PrivateElementFind (O, method.[[Key]])。 - 如果 entry 不是
empty ，则抛出一个TypeError 异常。 - 将 method 添加到 O.[[PrivateElements]]。
- 返回
unused 。
私有方法和访问器的值在实例之间是共享的。此操作不会创建方法或访问器的新副本。
7.3.29 HostEnsureCanAddPrivateElement ( O )
主机定义的抽象操作 HostEnsureCanAddPrivateElement 接受参数 O（一个对象），并返回一个包含正常完成的
HostEnsureCanAddPrivateElement 的实现必须符合以下要求：
- 如果 O 不是主机定义的外来对象，则此抽象操作必须返回
NormalCompletion (unused )，并且不执行其他步骤。 - 使用相同参数调用此抽象操作的任何两次必须返回相同类型的
完成记录 。
HostEnsureCanAddPrivateElement 的默认实现是返回
此抽象操作仅由 ECMAScript
7.3.30 PrivateGet ( O, P )
抽象操作 PrivateGet 接受参数 O（一个对象）和 P（一个私有名称），并返回一个包含 ECMAScript 语言值的普通完成或抛出完成。调用时执行以下步骤：
- 令 entry 为
PrivateElementFind (O, P)。 - 如果 entry 为空，则抛出 TypeError 异常。
- 如果 entry.[[Kind]] 是
field 或method ，则- 返回 entry.[[Value]]。
Assert ：确保 entry.[[Kind]] 是accessor 。- 如果 entry.[[Get]] 是
undefined ，则抛出 TypeError 异常。 - 令 getter 为 entry.[[Get]]。
- 返回 ?
Call (getter, O)。
7.3.31 PrivateSet ( O, P, value )
抽象操作 PrivateSet 接受参数 O（一个对象）、P（一个私有名称）和 value（一个 ECMAScript 语言值），并返回一个包含未使用的普通完成或抛出完成。调用时执行以下步骤：
- 令 entry 为
PrivateElementFind (O, P)。 - 如果 entry 为空，则抛出 TypeError 异常。
- 如果 entry.[[Kind]] 是
field ，则- 将 entry.[[Value]] 设置为 value。
- 否则，如果 entry.[[Kind]] 是
method ，则- 抛出 TypeError 异常。
- 否则，
- 返回
unused 。
7.3.32 DefineField ( receiver, fieldRecord )
抽象操作 DefineField 接受参数 receiver（一个对象）和 fieldRecord（一个
- 令 fieldName 为 fieldRecord.[[Name]]。
- 令 initializer 为 fieldRecord.[[Initializer]]。
- 如果 initializer 不为空，则
- 令 initValue 为 ?
Call (initializer, receiver)。
- 令 initValue 为 ?
- 否则，
- 令 initValue 为
undefined 。
- 令 initValue 为
- 如果 fieldName 是一个
Private Name ，则- 执行 ?
PrivateFieldAdd (receiver, fieldName, initValue)。
- 执行 ?
- 否则，
Assert : 确保IsPropertyKey (fieldName) 是true 。- 执行 ?
CreateDataPropertyOrThrow (receiver, fieldName, initValue)。
- 返回
unused 。
7.3.33 InitializeInstanceElements ( O, constructor )
抽象操作 InitializeInstanceElements 接受参数 O（一个对象）和 constructor（一个 ECMAScript
- 令 methods 为 constructor.[[PrivateMethods]] 的值。
- 对于每个
PrivateElement method 在 methods 中，执行- 执行 ?
PrivateMethodOrAccessorAdd (O, method)。
- 执行 ?
- 令 fields 为 constructor.[[Fields]] 的值。
- 对于每个元素 fieldRecord 在 fields 中，执行
- 执行 ?
DefineField (O, fieldRecord)。
- 执行 ?
- 返回
unused 。
7.3.34 AddValueToKeyedGroup ( groups, key, value )
抽象操作 AddValueToKeyedGroup 接受参数 groups（一个包含字段 [[Key]]（一个 ECMAScript
语言值）和 [[Elements]]（一个 ECMAScript 语言值列表）的
7.3.35 GroupBy ( items, callbackfn, keyCoercion )
抽象操作 GroupBy 接受参数 items（一个 ECMAScript 语言值）、callbackfn（一个 ECMAScript 语言值）和
keyCoercion（
- 执行 ?
RequireObjectCoercible (items). - 如果
IsCallable (callbackfn) 的结果为false ，则抛出一个TypeError 异常。 - 令 groups 为一个新的空
List 。 - 令 iteratorRecord 为 ?
GetIterator (items,sync ). - 令 k 为 0。
- 重复执行
- 如果 k ≥ 253 - 1，则
- 令 error 为
ThrowCompletion (一个新创建的TypeError 对象)。 - 返回 ?
IteratorClose (iteratorRecord, error).
- 令 error 为
- 令 next 为 ?
IteratorStepValue (iteratorRecord). - 如果 next 为
done ，则- 返回 groups。
- 令 value 为 next。
- 令 key 为
Completion (Call (callbackfn,undefined , « value,𝔽 (k) »)). IfAbruptCloseIterator (key, iteratorRecord).- 如果 keyCoercion 为
property ，则- 将 key 设置为
Completion (ToPropertyKey (key)). IfAbruptCloseIterator (key, iteratorRecord).
- 将 key 设置为
- 否则，
Assert : keyCoercion 为zero 。- 如果 key 是
-0 𝔽，则将 key 设置为+0 𝔽。
- 执行
AddValueToKeyedGroup (groups, key, value). - 将 k 设置为 k + 1。
- 如果 k ≥ 253 - 1，则
7.4 迭代器对象操作
请参阅通用迭代接口（
7.4.1 迭代器记录
迭代器记录是用于封装迭代器或异步迭代器及其 next 方法的
迭代器记录具有以下在
| 字段名 | 值 | 含义 |
|---|---|---|
| [[Iterator]] | 一个对象 | 符合 Iterator 或 AsyncIterator 接口的对象。 |
| [[NextMethod]] |
一个 |
[[Iterator]] 对象的 next 方法。
|
| [[Done]] | 一个布尔值 | 表示迭代器是否已关闭。 |
7.4.2 GetIteratorFromMethod ( obj, method )
抽象操作 GetIteratorFromMethod 接受参数 obj（一个
7.4.3 GetIterator ( obj, kind )
抽象操作 GetIterator 接受参数 obj（一个 ECMAScript 语言值）和 kind（
- 如果 kind 是
async ，则- 令 method 为 ?
GetMethod (obj,@@asyncIterator )。 - 如果 method 是
undefined ，则- 令 syncMethod 为 ?
GetMethod (obj,@@iterator )。 - 如果 syncMethod 是
undefined ，则抛出TypeError 异常。 - 令 syncIteratorRecord 为 ?
GetIteratorFromMethod (obj, syncMethod)。 - 返回
CreateAsyncFromSyncIterator (syncIteratorRecord)。
- 令 syncMethod 为 ?
- 令 method 为 ?
- 否则，
- 令 method 为 ?
GetMethod (obj,@@iterator )。
- 令 method 为 ?
- 如果 method 是
undefined ，则抛出TypeError 异常。 - 返回 ?
GetIteratorFromMethod (obj, method)。
7.4.4 IteratorNext ( iteratorRecord [ , value ] )
抽象操作 IteratorNext 接受参数 iteratorRecord（一个
7.4.5 IteratorComplete ( iterResult )
抽象操作 IteratorComplete 接受参数 iterResult（一个对象）并返回一个包含正常完成状态的布尔值或抛出异常完成状态。调用时执行以下步骤：
7.4.6 IteratorValue ( iterResult )
抽象操作 IteratorValue 接受参数 iterResult（一个对象）并返回一个包含正常完成状态的 ECMAScript 语言值或抛出异常完成状态。调用时执行以下步骤：
- 返回 ?
Get (iterResult,"value" )。
7.4.7 IteratorStep ( iteratorRecord )
抽象操作 IteratorStep 接受参数 iteratorRecord（一个
- 令 result 为 ?
IteratorNext (iteratorRecord). - 令 done 为 ?
IteratorComplete (result). - 如果 done 为
true ，则返回false 。 - 返回 result。
7.4.8 IteratorStepValue ( iteratorRecord )
抽象操作 IteratorStepValue 接受参数 iteratorRecord（一个
- 令 result 为
Completion (IteratorNext (iteratorRecord)). - If result is a
throw completion , 则- 将 iteratorRecord.[[Done]]
设置为
true 。 - 返回 ? result。
- 将 iteratorRecord.[[Done]]
设置为
- 将 result 设置为 ! result。
- 令 done 为
Completion (IteratorComplete (result)). - If done 是一个
throw completion , 则- 将 iteratorRecord.[[Done]]
设置为
true 。 - 返回 ? done。
- 将 iteratorRecord.[[Done]]
设置为
- 将 done 设置为 ! done。
- If done 是
true , 则- 将 iteratorRecord.[[Done]]
设置为
true 。 - 返回
done 。
- 将 iteratorRecord.[[Done]]
设置为
- 令 value 为
Completion (Get (result,"value" )). - If value 是一个
throw completion , 则- 将 iteratorRecord.[[Done]]
设置为
true 。
- 将 iteratorRecord.[[Done]]
设置为
- 返回 ? value。
7.4.9 IteratorClose ( iteratorRecord, completion )
抽象操作 IteratorClose 接受参数 iteratorRecord（一个
Assert ： iteratorRecord.[[Iterator]]是一个对象 。- 令 iterator 为 iteratorRecord.[[Iterator]]。
- 令 innerResult 为
Completion (GetMethod (iterator,"return" )). - 如果 innerResult 是一个
正常完成 ，则- 令 return 为 innerResult.[[Value]]。
- 如果 return 是
undefined ，则返回 ? completion。 - 将 innerResult 设置为
Completion (Call (return, iterator)).
- 如果 completion 是一个
抛出完成 ，则返回 ? completion。 - 如果 innerResult 是一个
抛出完成 ，则返回 ? innerResult。 - 如果 innerResult.[[Value]]
不是一个对象 ，则抛出TypeError 异常。 - 返回 ? completion。
7.4.10 IfAbruptCloseIterator ( value, iteratorRecord )
IfAbruptCloseIterator 是一个使用
IfAbruptCloseIterator (value, iteratorRecord).
意味着与以下内容相同：
Assert : value 是一个完成记录 。- 如果 value 是一个
突然完成 ，则返回 ?IteratorClose (iteratorRecord, value)。 - 否则，将 value 设置为 ! value。
7.4.11 AsyncIteratorClose ( iteratorRecord, completion )
异步抽象操作 AsyncIteratorClose 接受参数 iteratorRecord （一个
Assert : iteratorRecord.[[Iterator]]是一个对象 。- 让 iterator 为 iteratorRecord.[[Iterator]]。
- 让 innerResult 为
Completion (GetMethod (iterator,"return" ))。 - 如果 innerResult 是一个
正常完成 ，则：- 让 return 为 innerResult.[[Value]]。
- 如果 return 是
undefined ，返回 ? completion。 - 将 innerResult 设为
Completion (Call (return, iterator))。 - 如果 innerResult 是一个
正常完成 ， 将 innerResult 设为Completion (Await (innerResult.[[Value]]))。
- 如果 completion 是一个
抛出完成 ，返回 ? completion。 - 如果 innerResult 是一个
抛出完成 ，返回 ? innerResult。 - 如果 innerResult.[[Value]]
不是一个对象 ， 抛出TypeError 异常。 - 返回 ? completion。
7.4.12 CreateIterResultObject ( value, done )
抽象操作 CreateIterResultObject 接受参数 value （一个
- 让 obj 为
OrdinaryObjectCreate (%Object.prototype% )。 - 执行 !
CreateDataPropertyOrThrow (obj,"value" , value)。 - 执行 !
CreateDataPropertyOrThrow (obj,"done" , done)。 - 返回 obj。
7.4.13 CreateListIteratorRecord ( list )
抽象操作 CreateListIteratorRecord 接受参数 list （一个 next 方法返回
list 的连续元素。在调用时执行以下步骤：
- 让 closure 成为一个没有参数的新
Abstract Closure ，它捕获 list，并在调用时执行以下步骤：- 对于 list 的每个元素 E，执行
- 执行 ?
GeneratorYield (CreateIterResultObject (E,false ))。
- 执行 ?
- 返回
NormalCompletion (undefined )。
- 对于 list 的每个元素 E，执行
- 让 iterator 成为
CreateIteratorFromClosure (closure,empty ,%IteratorPrototype% )。 - 返回
Iterator Record { [[Iterator]]: iterator, [[NextMethod]]: %GeneratorFunction.prototype.prototype.next%, [[Done]]:false }。
列表迭代器对象对 ECMAScript 代码不可直接访问。
7.4.14 IteratorToList ( iteratorRecord )
抽象操作 IteratorToList 接受参数 iteratorRecord （一个
- 让 values 成为一个新的空
List 。 - 重复执行，
- 让 next 成为 ?
IteratorStepValue (iteratorRecord)。 - 如果 next 是
done ，那么- 返回 values。
- 将 next 追加到 values。
- 让 next 成为 ?
8 语法导向操作
除了本节中定义的操作外，专门的
8.1 运行时语义：评估
语法导向操作 Evaluation 不接受参数并返回一个
8.2 Scope 分析
8.2.1 静态语义：BoundNames
语法指导操作 BoundNames 不接受参数，并返回一个字符串列表（List）。
它在以下产生式上分段定义：
- 返回一个
List ，其唯一元素是Identifier 的字符串值，来自于Identifier 。
- 返回 «
"yield" »。
- 返回 «
"await" »。
- 返回
BoundNames 的结果， 来自于BindingList 。
- 令 names1 为
BoundNames 的结果， 来自于BindingList 。 - 令 names2 为
BoundNames 的结果， 来自于LexicalBinding 。 - 返回
list-concatenation 的结果， 包括 names1 和 names2。
- 返回
BoundNames 的结果， 来自于BindingIdentifier 。
- 返回
BoundNames 的结果， 来自于BindingPattern 。
- 令 names1 为
BoundNames 的结果， 来自于VariableDeclarationList 。 - 令 names2 为
BoundNames 的结果， 来自于VariableDeclaration 。 - 返回
list-concatenation 的结果， 包括 names1 和 names2。
- 返回
BoundNames 的结果， 来自于BindingIdentifier 。
- 返回
BoundNames 的结果， 来自于BindingPattern 。
- 返回一个新的空
List 。
- 让 names1 成为
BoundNames 的结果， 其中BindingPropertyList 是指向的非终结符。 - 让 names2 成为
BoundNames 的结果， 其中BindingRestProperty 是指向的非终结符。 - 返回
list-concatenation 的结果， 其中包含 names1 和 names2。
- 返回一个新的空
List 。
- 让 names 成为
BoundNames 的结果， 其中BindingRestElement 是指向的非终结符。
- 让 names1 成为
BoundNames 的结果， 其中BindingElementList 是指向的非终结符。 - 让 names2 成为
BoundNames 的结果， 其中BindingRestElement 是指向的非终结符。 - 返回
list-concatenation 的结果， 其中包含 names1 和 names2。
- 让 names1 成为
BoundNames 的结果， 其中BindingPropertyList 是指向的非终结符。 - 让 names2 成为
BoundNames 的结果， 其中BindingProperty 是指向的非终结符。 - 返回
list-concatenation 的结果， 其中包含 names1 和 names2。
- 让 names1 成为
BoundNames 的结果， 其中BindingElementList 是指向的非终结符。 - 让 names2 成为
BoundNames 的结果， 其中BindingElisionElement 是指向的非终结符。 - 返回
list-concatenation 的结果， 其中包含 names1 和 names2。
- 返回
BoundNames 的结果， 其中BindingElement 是指向的非终结符。
- 返回
BoundNames 的结果， 其中BindingElement 是指向的非终结符。
- 返回
BoundNames 的结果， 其中BindingIdentifier 是指向的非终结符。
- 返回
BoundNames 的结果， 其中BindingPattern 是指向的非终结符。
- 返回
BoundNames 的结果， 其中ForBinding 是指向的非终结符。
- 返回
BoundNames 的结果， 其中BindingIdentifier 是指向的非终结符。
- 返回«
"*default*" »。
- 返回一个新的空
List 。
- 将 names1 设置为获取
FormalParameterList 的BoundNames 。 - 将 names2 设置为获取
FunctionRestParameter 的BoundNames 。 - 返回
list-concatenation 的结果，即 names1 和 names2 的连接列表。
- 将 names1 设置为获取
FormalParameterList 的BoundNames 。 - 将 names2 设置为获取
FormalParameter 的BoundNames 。 - 返回
list-concatenation 的结果，即 names1 和 names2 的连接列表。
- 将 formals 设置为由
ArrowFormalParameters 覆盖的CoverParenthesizedExpressionAndArrowParameterList 。 - 返回 formals 的
BoundNames 。
- 返回
BindingIdentifier 的绑定名称。
- 返回
"*default*" 。
- 返回
BindingIdentifier 的BoundNames 。
- 返回 «
"*default*" »。
- 返回 «
"*default*" »。
- 返回 «
"*default*" »。
- 令head为被
CoverCallExpressionAndAsyncArrowHead 覆盖的AsyncArrowHead 。 - 返回head的
BoundNames 。
- 返回一个新的空
List 。
- 让names1为
BoundNames ：ImportedDefaultBinding 的BoundNames 。 - 让names2为
BoundNames ：NameSpaceImport 的BoundNames 。 - 返回
list-concatenation 的names1和names2。
- 让names1为
BoundNames ：ImportedDefaultBinding 的BoundNames 。 - 让names2为
BoundNames ：NamedImports 的BoundNames 。 - 返回
list-concatenation 的names1和names2。
- 返回一个新的空
List 。
- 让names1为
BoundNames ：ImportsList 的BoundNames 。 - 让names2为
BoundNames ：ImportSpecifier 的BoundNames 。 - 返回
list-concatenation 的names1和names2。
- 返回一个新的空
List 。
- 令declarationNames为
HoistableDeclaration 的BoundNames 。 - 如果declarationNames不包含元素
"*default*" ，则将"*default*" 添加到declarationNames中。 - 返回declarationNames。
- 令declarationNames为
ClassDeclaration 的BoundNames 。 - 如果declarationNames不包含元素
"*default*" ，则将"*default*" 添加到declarationNames中。 - 返回declarationNames。
- 返回«
"*default*" »。
8.2.2 静态语义：DeclarationPart
DeclarationPart 是一个语法指导操作，不接受参数并返回一个解析节点（Parse Node）。它根据以下产生式逐段定义：
- 返回
ClassDeclaration 。
8.2.3 静态语义：IsConstantDeclaration
- 返回
false 。
- 返回
true 。
- 返回
false 。
- 返回
false 。
- 返回
false 。
没有必要将 export default
8.2.4 静态语义：词法声明的名称
- 返回一个新的空
列表 。
- 令 names1 为
LexicallyDeclaredNames 的StatementList 。 - 令 names2 为
LexicallyDeclaredNames 的StatementListItem 。 - 返回 names1 和 names2 的
列表连接 。
- 如果
Statement 是Statement : LabelledStatement LexicallyDeclaredNames 的LabelledStatement 。 - 返回一个新的空
列表 。
- 返回
BoundNames 的Declaration 。
- 返回一个新的空
列表 。
- 如果第一个
CaseClauses 存在，令names1为第一个CaseClauses 的LexicallyDeclaredNames 。 - 否则，令names1为一个新的空
列表 。 - 令names2为
DefaultClause 的LexicallyDeclaredNames 。 - 如果第二个
CaseClauses 存在，令names3为第二个CaseClauses 的LexicallyDeclaredNames 。 - 否则，令names3为一个新的空
列表 。 - 返回names1、names2和names3的
列表连接 。
- 令 names1 为
LexicallyDeclaredNames 的CaseClauses 。 - 令 names2 为
LexicallyDeclaredNames 的CaseClause 。 - 返回 names1 和 names2 的
列表连接 。
- 如果
StatementList 存在，返回StatementList 的LexicallyDeclaredNames 。 - 返回一个新的空
列表 。
- 如果
StatementList 存在，返回StatementList 的LexicallyDeclaredNames 。 - 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
在
- 令 names1 为
LexicallyDeclaredNames 的ModuleItemList 。 - 令 names2 为
LexicallyDeclaredNames 的ModuleItem 。 - 返回 names1 和 names2 的
列表连接 。
- 如果
ExportDeclaration 是exportVariableStatement ，返回一个新的空列表 。 - 返回
BoundNames 的ExportDeclaration 。
在
8.2.5 静态语义：词法作用域声明
- 令 declarations1 为
LexicallyScopedDeclarations 的StatementList 。 - 令 declarations2 为
LexicallyScopedDeclarations 的StatementListItem 。 - 返回 declarations1 和 declarations2 的
列表连接 。
- 如果
Statement 是Statement : LabelledStatement LexicallyScopedDeclarations 的LabelledStatement 。 - 返回一个新的空
列表 。
- 返回一个
列表 ，其唯一元素是DeclarationPart 的Declaration 。
- 返回一个新的空
列表 。
- 如果第一个
CaseClauses 存在，令declarations1为第一个CaseClauses 的LexicallyScopedDeclarations 。 - 否则，令declarations1为一个新的空
列表 。 - 令declarations2为
DefaultClause 的LexicallyScopedDeclarations 。 - 如果第二个
CaseClauses 存在，令declarations3为第二个CaseClauses 的LexicallyScopedDeclarations 。 - 否则，令declarations3为一个新的空
列表 。 - 返回declarations1、declarations2和declarations3的
列表连接 。
- 令 declarations1 为
LexicallyScopedDeclarations 的CaseClauses 。 - 令 declarations2 为
LexicallyScopedDeclarations 的CaseClause 。 - 返回 declarations1 和 declarations2 的
列表连接 。
- 如果
StatementList 存在，返回StatementList 的LexicallyScopedDeclarations 。 - 返回一个新的空
列表 。
- 如果
StatementList 存在，返回StatementList 的LexicallyScopedDeclarations 。 - 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回 «
FunctionDeclaration »。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 令 declarations1 为
LexicallyScopedDeclarations 的ModuleItemList 。 - 令 declarations2 为
LexicallyScopedDeclarations 的ModuleItem 。 - 返回 declarations1 和 declarations2 的
列表连接 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回一个
列表 ，其唯一元素是DeclarationPart 的Declaration 。
- 返回一个
列表 ，其唯一元素是DeclarationPart 的HoistableDeclaration 。
- 返回一个
列表 ，其唯一元素是ClassDeclaration 。
- 返回一个
列表 ，其唯一元素是此ExportDeclaration 。
8.2.6 静态语义: VarDeclaredNames
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 令 names1 为
VarDeclaredNames 的StatementList 。 - 令 names2 为
VarDeclaredNames 的StatementListItem 。 - 返回 names1 和 names2 的
列表连接 。
- 返回一个新的空
列表 。
- 令 names1 为第一个
VarDeclaredNames 的Statement 。 - 令 names2 为第二个
VarDeclaredNames 的Statement 。 - 返回 names1 和 names2 的
列表连接 。
- 令 names1 为
BoundNames 的VariableDeclarationList 。 - 令 names2 为
VarDeclaredNames 的Statement 。 - 返回 names1 和 names2 的
列表连接 。
- 令 names1 为
BoundNames 的ForBinding 。 - 令 names2 为
VarDeclaredNames 的Statement 。 - 返回 names1 和 names2 的
列表连接 。
本节由附录
- 返回一个新的空
列表 。
- 如果第一个
CaseClauses 存在，令names1为第一个CaseClauses 的VarDeclaredNames 。 - 否则，令names1为一个新的空
列表 。 - 令names2为
DefaultClause 的VarDeclaredNames 。 - 如果第二个
CaseClauses 存在，令names3为第二个CaseClauses 的VarDeclaredNames 。 - 否则，令names3为一个新的空
列表 。 - 返回names1、names2和names3的
列表连接 。
- 令 names1 为
VarDeclaredNames 的CaseClauses 。 - 令 names2 为
VarDeclaredNames 的CaseClause 。 - 返回 names1 和 names2 的
列表连接 。
- 如果
StatementList 存在，返回StatementList 的VarDeclaredNames 。 - 返回一个新的空
列表 。
- 如果
StatementList 存在，返回StatementList 的VarDeclaredNames 。 - 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 令 names1 为
VarDeclaredNames 的Block 。 - 令 names2 为
VarDeclaredNames 的Catch 。 - 返回 names1 和 names2 的
列表连接 。
- 令 names1 为
VarDeclaredNames 的Block 。 - 令 names2 为
VarDeclaredNames 的Finally 。 - 返回 names1 和 names2 的
列表连接 。
- 令 names1 为
VarDeclaredNames 的Block 。 - 令 names2 为
VarDeclaredNames 的Catch 。 - 令 names3 为
VarDeclaredNames 的Finally 。 - 返回 names1、names2 和 names3 的
列表连接 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 返回一个新的空
列表 。
- 令 names1 为
VarDeclaredNames 的ModuleItemList 。 - 令 names2 为
VarDeclaredNames 的ModuleItem 。 - 返回 names1 和 names2 的
列表连接 。
- 返回一个新的空
列表 。
- 如果
ExportDeclaration 是exportVariableStatement ，返回BoundNames 的ExportDeclaration 。 - 返回一个新的空
列表 。
8.2.7 静态语义：VarScopedDeclarations
VarScopedDeclarations是一个无需参数并返回
- 返回一个新的空
List 。
- 返回一个新的空
List 。
- 令 declarations1 为
VarScopedDeclarations ，位于StatementList 。 - 令 declarations2 为
VarScopedDeclarations ，位于StatementListItem 。 - 返回
list-concatenation 的结果，包括 declarations1 和 declarations2。
- 返回一个新的空
List 。
- 返回 «
VariableDeclaration »。
- 令 declarations1 为
VarScopedDeclarations 的VariableDeclarationList 。 - 返回
list-concatenation 的 declarations1 和 «VariableDeclaration »。
- 令 declarations1 为
VarScopedDeclarations 的第一个Statement 。 - 令 declarations2 为
VarScopedDeclarations 的第二个Statement 。 - 返回
list-concatenation 的 declarations1 和 declarations2。
- 让 declarations1 成为
VariableDeclarationList 的VarScopedDeclarations 。 - 让 declarations2 成为
Statement 的VarScopedDeclarations 。 - 返回 declarations1 和 declarations2 的
list-concatenation 。
- 令 declarations1 为 «
ForBinding »。 - 令 declarations2 为
VarScopedDeclarations 在Statement 中的结果。 - 返回 declarations1 和 declarations2 的
list-concatenation 。
本节由附件
- 返回一个新的空
列表 。
- 如果第一个
CaseClauses 存在，则让declarations1成为第一个CaseClauses 的VarScopedDeclarations 。 - 否则，让declarations1成为一个新的空
列表 。 - 让declarations2成为
VarScopedDeclarations 的DefaultClause 。 - 如果第二个
CaseClauses 存在，则让declarations3成为第二个CaseClauses 的VarScopedDeclarations 。 - 否则，让declarations3成为一个新的空
列表 。 - 返回declarations1，declarations2和declarations3的
列表连接 。
- 让declarations1成为
VarScopedDeclarations 的CaseClauses 。 - 让declarations2成为
VarScopedDeclarations 的CaseClause 。 - 返回declarations1和declarations2的
列表连接 。
- 如果
StatementList 存在， 返回VarScopedDeclarations 的StatementList 。 - 返回一个新的空
List 。
- 如果
StatementList 存在， 返回VarScopedDeclarations 的StatementList 。 - 返回一个新的空
List 。
- 返回一个新的空
List 。
- 让declarations1为
VarScopedDeclarations 的Block 。 - 让declarations2为
VarScopedDeclarations 的Catch 。 - 返回declarations1和declarations2的
list-concatenation 。
- 返回一个新的空
List 。
- 返回一个新的空
List 。
- 返回一个新的空
List 。
- 返回一个新的空
List 。
- 返回一个新的空
List 。
- 返回一个新的空
List 。
- 让declarations1成为
VarScopedDeclarations 的ModuleItemList 。 - 让declarations2成为
VarScopedDeclarations 的ModuleItem 。 - 返回
list-concatenation 的declarations1和declarations2。
- 返回一个新的空
List 。
- 如果
ExportDeclaration 是exportVariableStatement ，返回VarScopedDeclarations 的VariableStatement 。 - 返回一个新的空
List 。
8.2.8 静态语义: TopLevelLexicallyDeclaredNames
- 将names1设为
StatementList 的顶层词法声明名称。 - 将names2设为
StatementListItem 的顶层词法声明名称。 - 返回names1和names2的
列表连接 。
- 返回一个新的空
List 。
- 如果
Declaration 是Declaration : HoistableDeclaration - 返回一个新的空
List 。
- 返回一个新的空
- 返回
BoundNames ，属于Declaration 。
在函数或脚本的顶层，函数声明被视为 var 声明，而不是词法声明。
8.2.9 静态语义: TopLevelLexicallyScopedDeclarations
静态语义操作 TopLevelLexicallyScopedDeclarations 不接受参数，并返回一个
- 让 declarations1 成为
TopLevelLexicallyScopedDeclarations 的StatementList 。 - 让 declarations2 成为
TopLevelLexicallyScopedDeclarations 的StatementListItem 。 - 返回
list-concatenation ， 包含 declarations1 和 declarations2。
- 返回一个新的空
List 。
- 如果
Declaration 是Declaration : HoistableDeclaration - 返回一个新的空
List 。
- 返回一个新的空
- 返回 «
Declaration »。
8.2.10 静态语义: TopLevelVarDeclaredNames
语法定向操作 TopLevelVarDeclaredNames 不接受参数，并返回一个
- 令 names1 为
TopLevelVarDeclaredNames 是StatementList 的。 - 令 names2 为
TopLevelVarDeclaredNames 是StatementListItem 的。 - 返回
list-concatenation 的 names1 和 names2。
- 如果
Declaration 是Declaration : HoistableDeclaration - 返回一个新的空
List 。
- 如果
Statement 是Statement : LabelledStatement TopLevelVarDeclaredNames 的Statement 。 - 返回
VarDeclaredNames 的Statement 。
在函数或脚本的顶层，内部函数声明被视为 var 声明。
8.2.11 Static Semantics: TopLevelVarScopedDeclarations
The
- Let declarations1 be
TopLevelVarScopedDeclarations 的StatementList 。 - Let declarations2 be
TopLevelVarScopedDeclarations 的StatementListItem 。 - Return
列表连接 declarations1 和 declarations2。
- 如果
Declaration 是Declaration : HoistableDeclaration - 让 declaration 成为
HoistableDeclaration 的DeclarationPart 。 - 返回 « declaration »。
- 让 declaration 成为
- 返回一个新的空
List 。
- 如果
Statement 是Statement : LabelledStatement TopLevelVarScopedDeclarations 中的Statement 。 - 返回
VarScopedDeclarations 中的Statement 。
- 返回 «
FunctionDeclaration »。
8.3 Labels
8.3.1 静态语义: 包含重复标签 (ContainsDuplicateLabels)
- 返回
false 。
- 令 hasDuplicates 为带有参数 labelSet 的
ContainsDuplicateLabels 在StatementList 中的结果。 - 如果 hasDuplicates 是
true ，则返回true 。 - 返回带有参数 labelSet 的
ContainsDuplicateLabels 在StatementListItem 中的结果。
- 令 hasDuplicate 为带有参数 labelSet 的
ContainsDuplicateLabels 在第一个Statement 中的结果。 - 如果 hasDuplicate 是
true ，则返回true 。 - 返回带有参数 labelSet 的
ContainsDuplicateLabels 在第二个Statement 中的结果。
- 返回带有参数 labelSet 的
ContainsDuplicateLabels 在Statement 中的结果。
- 返回带有参数 labelSet 的
ContainsDuplicateLabels 在Statement 中的结果。
- 返回带有参数 labelSet 的
ContainsDuplicateLabels 在Statement 中的结果。
- 返回带有参数 labelSet 的
ContainsDuplicateLabels 在Statement 中的结果。
- 返回带有参数 labelSet 的
ContainsDuplicateLabels 在Statement 中的结果。
此部分由附录
- 返回带有参数 labelSet 的
ContainsDuplicateLabels 的Statement 。
- 返回带有参数 labelSet 的
ContainsDuplicateLabels 的CaseBlock 。
- 返回
false 。
- 如果第一个
CaseClauses 存在，则- 如果使用参数 labelSet 调用第一个
CaseClauses 的ContainsDuplicateLabels 返回true ，则返回true 。
- 如果使用参数 labelSet 调用第一个
- 如果使用参数 labelSet 调用
ContainsDuplicateLabels 返回第二个DefaultClause 的结果为true ，则返回true 。 - 如果第二个
CaseClauses 不存在，则返回false 。 - 返回使用参数 labelSet 调用第二个
CaseClauses 的ContainsDuplicateLabels 。
- 令 hasDuplicates 为使用参数 labelSet 调用
ContainsDuplicateLabels 的结果，作用于CaseClauses 。 - 如果 hasDuplicates 为
true ，则返回true 。 - 返回使用参数 labelSet 调用
ContainsDuplicateLabels 的结果，作用于CaseClause 。
- 如果存在
StatementList ，则返回使用参数 labelSet 调用ContainsDuplicateLabels 的结果，作用于StatementList 。 - 返回
false 。
- 如果存在
StatementList ，则返回使用参数 labelSet 调用ContainsDuplicateLabels 的结果，作用于StatementList 。 - 返回
false 。
- 将 label 设置为
StringValue 的值，来源于LabelIdentifier 。 - 如果 labelSet 包含 label，则返回
true 。 - 令 newLabelSet 为
list-concatenation ，包含 labelSet 和 « label »。 - 返回使用参数 newLabelSet 调用
ContainsDuplicateLabels 的结果，作用于LabelledItem 。
- 返回
false 。
- 让 hasDuplicates 成为
ContainsDuplicateLabels 用参数 labelSet 计算Block 。 - 如果 hasDuplicates 是
true ，则返回true 。 - 返回
ContainsDuplicateLabels 用参数 labelSet 计算Catch 。
- 让 hasDuplicates 成为
ContainsDuplicateLabels 用参数 labelSet 计算Block 。 - 如果 hasDuplicates 是
true ，则返回true 。 - 返回
ContainsDuplicateLabels 用参数 labelSet 计算Finally 。
- 如果
ContainsDuplicateLabels 用参数 labelSet 计算Block 的结果是true ，则返回true 。 - 如果
ContainsDuplicateLabels 用参数 labelSet 计算Catch 的结果是true ，则返回true 。 - 返回
ContainsDuplicateLabels 用参数 labelSet 计算Finally 的结果。
- 返回
ContainsDuplicateLabels 用参数 labelSet 计算Block 的结果。
- 返回
false 。
- 返回
false .
- 令 hasDuplicates 为带有参数 labelSet 的
ContainsDuplicateLabels ， 其中ModuleItemList 。 - 如果 hasDuplicates 为
true ，则返回true 。 - 返回带有参数 labelSet 的
ContainsDuplicateLabels ，其对应ModuleItem 。
- 返回
false 。
8.3.2 静态语义: ContainsUndefinedBreakTarget
语法定向操作 ContainsUndefinedBreakTarget 接受参数 labelSet（一个字符串
- 返回
false 。
- 让 hasUndefinedLabels 成为
ContainsUndefinedBreakTarget 应用于参数为 labelSet 的StatementList 。 - 如果 hasUndefinedLabels 是
true ，则返回true 。 - 返回
ContainsUndefinedBreakTarget 应用于参数为 labelSet 的StatementListItem 。
- 让 hasUndefinedLabels 成为
ContainsUndefinedBreakTarget 应用于参数为 labelSet 的第一个Statement 。 - 如果 hasUndefinedLabels 是
true ，则返回true 。 - 返回
ContainsUndefinedBreakTarget 应用于参数为 labelSet 的第二个Statement 。
- 返回
ContainsUndefinedBreakTarget 应用于参数为 labelSet 的Statement 。
- 返回
ContainsUndefinedBreakTarget 应用于参数为 labelSet 的Statement 。
- 返回
ContainsUndefinedBreakTarget 应用于参数为 labelSet 的Statement 。
- 返回
ContainsUndefinedBreakTarget 应用于参数为 labelSet 的Statement 。
- 返回
ContainsUndefinedBreakTarget 应用于参数为 labelSet 的Statement 。
此部分由附件
- 返回
false 。
- 如果 labelSet 不包含
StringValue 的LabelIdentifier ，则返回true 。 - 返回
false 。
- 返回
ContainsUndefinedBreakTarget 应用于参数为 labelSet 的Statement 。
- 返回
ContainsUndefinedBreakTarget 应用于参数为 labelSet 的CaseBlock 。
- 返回
false 。
- 如果第一个
CaseClauses 存在，则- 如果使用参数labelSet调用
ContainsUndefinedBreakTarget 返回true 。
- 如果使用参数labelSet调用
- 如果使用参数labelSet调用
ContainsUndefinedBreakTarget 的返回值为true ，则返回true 。 - 如果第二个
CaseClauses 不存在，则返回false 。 - 返回使用参数labelSet调用
ContainsUndefinedBreakTarget 的第二个CaseClauses 。
- 令hasUndefinedLabels为
ContainsUndefinedBreakTarget 的返回值，使用参数labelSet调用CaseClauses 。 - 如果hasUndefinedLabels为
true ，则返回true 。 - 使用参数labelSet调用
ContainsUndefinedBreakTarget 的返回值，使用CaseClause 。
- 如果存在
StatementList ，则返回使用参数labelSet调用ContainsUndefinedBreakTarget 的返回值，使用StatementList 。 - 返回
false 。
- 如果
StatementList 存在， 使用参数labelSet调用ContainsUndefinedBreakTarget 的返回值，使用StatementList 。 - 返回
false 。
- 令label为
StringValue 的返回值， 使用LabelIdentifier 。 - 令newLabelSet为
list-concatenation 的返回值，使用labelSet和«label »。 - 使用参数newLabelSet调用
ContainsUndefinedBreakTarget 的返回值， 使用LabelledItem 。
- 返回
false 。
- 令hasUndefinedLabels为
ContainsUndefinedBreakTarget 的返回值， 使用Block 和labelSet。 - 如果hasUndefinedLabels为
true ，返回true 。 - 使用
Catch 和labelSet调用ContainsUndefinedBreakTarget 的返回值。
- 令hasUndefinedLabels为
ContainsUndefinedBreakTarget 的返回值， 使用Block 和labelSet。 - 如果hasUndefinedLabels为
true ，返回true 。 - 使用
Finally 和labelSet调用ContainsUndefinedBreakTarget 的返回值。
- 如果
ContainsUndefinedBreakTarget 的返回值为true ，使用Block 和labelSet，返回true 。 - 如果
ContainsUndefinedBreakTarget 的返回值为true ，使用Catch 和labelSet，返回true 。 - 使用
Finally 和labelSet调用ContainsUndefinedBreakTarget 的返回值。
- 使用
Block 和labelSet调用ContainsUndefinedBreakTarget 的返回值。
- 返回
false 。
- 返回
false 。
- 让hasUndefinedLabels为
ContainsUndefinedBreakTarget 的返回值，使用ModuleItemList 和labelSet作为参数。 - 如果hasUndefinedLabels为
true ，返回true 。 - 使用
ModuleItem 和labelSet作为参数，调用ContainsUndefinedBreakTarget 的返回值。
- 返回
false 。
8.3.3 静态语义: ContainsUndefinedContinueTarget
语法定向操作 ContainsUndefinedContinueTarget 接受参数 iterationSet（一个字符串
- 返回
false 。
- 返回
ContainsUndefinedContinueTarget 对于BlockStatement 的结果，参数为 iterationSet 和 « »。
- 令 newIterationSet 为
list-concatenation 的结果，参数为 iterationSet 和 labelSet。 - 返回
ContainsUndefinedContinueTarget 对于IterationStatement 的结果，参数为 newIterationSet 和 « »。
- 令 hasUndefinedLabels 为
ContainsUndefinedContinueTarget 对于StatementList 的结果，参数为 iterationSet 和 « »。 - 如果 hasUndefinedLabels 是
true ，则返回true 。 - 返回
ContainsUndefinedContinueTarget 对于第二个Statement 的结果，参数为 iterationSet 和 « »。
- 令 hasUndefinedLabels 为
ContainsUndefinedContinueTarget 对于第一个Statement 的结果，参数为 iterationSet 和 « »。 - 如果 hasUndefinedLabels 是
true ，则返回true 。 - 返回
ContainsUndefinedContinueTarget 对于第二个Statement 的结果，参数为 iterationSet 和 « »。
- 返回
ContainsUndefinedContinueTarget 对于Statement 的结果，参数为 iterationSet 和 « »。
- 返回
ContainsUndefinedContinueTarget 对于Statement 的结果，参数为 iterationSet 和 « »。
- 返回
ContainsUndefinedContinueTarget 对于Statement 的结果，参数为 iterationSet 和 « »。
- 返回使用参数 iterationSet 和 « » 的
ContainsUndefinedContinueTarget 对Statement 进行调用。
- 返回使用参数 iterationSet 和 « » 的
ContainsUndefinedContinueTarget 对Statement 进行调用。
本节由附录
- 返回
false 。
- 如果 iterationSet 不包含
LabelIdentifier 的StringValue ，则返回true 。 - 返回
false 。
- 返回使用参数 iterationSet 和 « » 的
ContainsUndefinedContinueTarget 对Statement 进行调用。
- 返回使用参数 iterationSet 和 « » 的
ContainsUndefinedContinueTarget 对CaseBlock 进行调用。
- 返回
false 。
- 如果第一个
CaseClauses 存在，则- 如果
ContainsUndefinedContinueTarget 对第一个带参数 iterationSet 和 « » 的CaseClauses 返回true ，则返回true 。
- 如果
- 如果
ContainsUndefinedContinueTarget 对带参数 iterationSet 和 « » 的DefaultClause 返回true ，则返回true 。 - 如果第二个
CaseClauses 不存在，则返回false 。 - 返回使用参数 iterationSet 和 « » 的第二个
CaseClauses 的ContainsUndefinedContinueTarget 。
- 令 hasUndefinedLabels 等于使用参数 iterationSet 和
« » 的
ContainsUndefinedContinueTarget 对CaseClauses 进行调用。 - 如果 hasUndefinedLabels 是
true ，则返回true 。 - 返回使用参数 iterationSet 和 « » 的
ContainsUndefinedContinueTarget 对CaseClause 进行调用。
- 如果存在
StatementList ，则返回使用参数 iterationSet 和 « » 的ContainsUndefinedContinueTarget 对StatementList 进行调用。 - 返回
false 。
- 如果存在
StatementList ，则返回使用参数 iterationSet 和 « » 的ContainsUndefinedContinueTarget 对StatementList 进行调用。 - 返回
false 。
- 令 label 为
LabelIdentifier 的StringValue 。 - 令 newLabelSet 为 labelSet 和 «
label » 的
list-concatenation 。 - 返回使用参数 iterationSet 和 newLabelSet 的
ContainsUndefinedContinueTarget 对LabelledItem 进行调用。
- 返回
false 。
- 令 hasUndefinedLabels 为使用参数 iterationSet 和
« »
调用
ContainsUndefinedContinueTarget 对Block 的结果。 - 如果 hasUndefinedLabels 是
true ，则返回true 。 - 返回使用参数 iterationSet 和 « » 调用
ContainsUndefinedContinueTarget 对Catch 的结果。
- 令 hasUndefinedLabels 为使用参数 iterationSet 和
« »
调用
ContainsUndefinedContinueTarget 对Block 的结果。 - 如果 hasUndefinedLabels 是
true ，则返回true 。 - 返回使用参数 iterationSet 和 « » 调用
ContainsUndefinedContinueTarget 对Finally 的结果。
- 如果使用参数 iterationSet 和 « » 调用
ContainsUndefinedContinueTarget 对Block 的结果为true ，则返回true 。 - 如果使用参数 iterationSet 和 « » 调用
ContainsUndefinedContinueTarget 对Catch 的结果为true ，则返回true 。 - 返回使用参数 iterationSet 和 « » 调用
ContainsUndefinedContinueTarget 对Finally 的结果。
- 返回使用参数 iterationSet 和 « » 调用
ContainsUndefinedContinueTarget 对Block 的结果。
- 返回
false 。
- 返回
false 。
- 让 hasUndefinedLabels 成为使用参数 iterationSet 和
« » 调用
ContainsUndefinedContinueTarget 对ModuleItemList 的结果。 - 如果 hasUndefinedLabels 是
true ，则返回true 。 - 返回使用参数 iterationSet 和 « » 调用
ContainsUndefinedContinueTarget 对ModuleItem 的结果。
- 返回
false 。
8.4 函数名称推断
8.4.1 静态语义：HasName
- 令 expr 为
ParenthesizedExpression ，它被CoverParenthesizedExpressionAndArrowParameterList 覆盖 。 - 如果 expr 的
IsFunctionDefinition 为false ，则返回false 。 - 返回 expr 的
HasName 。
- 返回
false 。
- 返回
true .
8.4.2 静态语义：IsFunctionDefinition
- 令 expr 为
ParenthesizedExpression ，它是由CoverParenthesizedExpressionAndArrowParameterList 覆盖 的表达式。 - 返回 expr 的
IsFunctionDefinition 。
- 返回
false .
- 返回
true .
8.4.3 静态语义：IsAnonymousFunctionDefinition ( expr )
抽象操作 IsAnonymousFunctionDefinition 接受参数 expr（一个
- 如果 expr 的
IsFunctionDefinition 返回false ，则返回false 。 - 令 hasName 为 expr 的
HasName 。 - 如果 hasName 返回
true ，则返回false 。 - 返回
true 。
8.4.4 静态语义：IsIdentifierRef
- 返回
true .
- 返回
false .
8.4.5 运行时语义：NamedEvaluation
- 令 expr 为
ParenthesizedExpression ，它被覆盖 在CoverParenthesizedExpressionAndArrowParameterList 中。 - 返回 ?
NamedEvaluation 以 name 作为参数调用 expr。
断言 :IsAnonymousFunctionDefinition (Expression ) 为true 。- 返回 ?
NamedEvaluation 以 name 作为参数调用Expression 。
- 返回
InstantiateOrdinaryFunctionExpression 以 name 作为参数调用FunctionExpression 。
- 返回
InstantiateGeneratorFunctionExpression 以 name 作为参数调用GeneratorExpression 。
- 返回
InstantiateAsyncGeneratorFunctionExpression 以 name 作为参数调用AsyncGeneratorExpression 。
- 返回
InstantiateAsyncFunctionExpression 以 name 作为参数调用AsyncFunctionExpression 。
- 返回
InstantiateArrowFunctionExpression 以 name 作为参数调用ArrowFunction 。
- 返回
InstantiateAsyncArrowFunctionExpression 以 name 作为参数调用AsyncArrowFunction 。
- 令 value 为 ?
ClassDefinitionEvaluation 以ClassTail 和参数undefined 以及 name 调用。 - 将 value.[[SourceText]] 设置为
与 ClassExpression 匹配的源文本。 - 返回 value。
8.5 包含
8.5.1 静态语义：Contains
本规范中未列出的每个语法生成替代方案都隐含具有以下默认的 Contains 定义：
-
返回
false 。
依赖于子结构的静态语义规则通常不会深入查看函数定义。
- 如果 symbol 是
ClassBody ，则返回true 。 - 如果 symbol 是
ClassHeritage ，则- 如果
ClassHeritage 存在，则返回true ；否则返回false 。
- 如果
- 如果
ClassHeritage 存在，则- 如果
ClassHeritage Contains symbol 是true ，则返回true 。
- 如果
- 返回
ComputedPropertyContains 的结果，其参数为 symbol，在ClassBody 中。
Static semantic rules that depend upon substructure generally do not look into class bodies except
for
- 返回
false 。
依赖子结构的静态语义规则通常不会检查static初始化块。
- 如果 symbol 不是
NewTarget 、SuperProperty 、SuperCall 、super或this之一，则返回false 。 - 如果
ArrowParameters Contains symbol 为true ，则返回true 。 - 返回
ConciseBody Contains symbol。
- 让 formals 为
ArrowFormalParameters ，该CoverParenthesizedExpressionAndArrowParameterList 被覆盖 。 - 返回 formals
Contains symbol 的结果。
- 如果 symbol 不是以下之一：
NewTarget ，SuperProperty ，SuperCall ，super，或this，返回false 。 - 返回
AsyncConciseBody 的Contains symbol 的结果。
- 如果 symbol 不是以下之一：
NewTarget ，SuperProperty ，SuperCall ，super，或this，返回false 。 - 令 head 为
AsyncArrowHead ，它被CoverCallExpressionAndAsyncArrowHead 覆盖 。 - 如果 head
Contains symbol 的结果为true ，返回true 。 - 返回
AsyncConciseBody Contains symbol 的结果。
Contains is used to detect new.target, this, and super usage
within an
- 如果 symbol 是
MethodDefinition ，返回true 。 - 返回
MethodDefinition ComputedPropertyContains symbol 的结果。
- 返回
false 。
- 如果
MemberExpression Contains symbol 是true ，返回true 。 - 返回
false 。
- 如果 symbol 是
ReservedWord super，返回true 。 - 返回
false 。
- 如果
CallExpression Contains symbol 是true ，返回true 。 - 返回
false 。
- 返回
false 。
- 如果
OptionalChain Contains symbol 是true ，返回true 。 - 返回
false 。
8.5.2 静态语义：ComputedPropertyContains
- 返回
false 。
- 返回
ComputedPropertyName 的结果，其中 symbol 被作为Contains 的参数。
- 返回
ComputedPropertyContains 的结果，其中ClassElementName 被作为参数 symbol。
- 返回
ComputedPropertyContains 的结果，其中ClassElementName 被作为参数 symbol。
- 返回
ComputedPropertyContains 的结果，其中ClassElementName 被作为参数 symbol。
- 令 inList 为
ComputedPropertyContains 的结果，其中ClassElementList 被作为参数 symbol。 - 如果 inList 为
true ，则返回true 。 - 返回
ComputedPropertyContains 的结果，其中ClassElement 被作为参数 symbol。
- 返回
false 。
- 返回
false 。
- 返回
ComputedPropertyContains 的结果，其中ClassElementName 被作为参数 symbol。
- 返回
ComputedPropertyContains 的结果，其中ClassElementName 被作为参数 symbol。
8.6 杂项
这些操作在整个规范的多个地方使用。
8.6.1 运行时语义: InstantiateFunctionObject
- 返回
InstantiateOrdinaryFunctionObject 对FunctionDeclaration 的调用，参数为 env 和 privateEnv。
- 返回
InstantiateGeneratorFunctionObject 对GeneratorDeclaration 的调用，参数为 env 和 privateEnv。
- 返回
InstantiateAsyncGeneratorFunctionObject 对AsyncGeneratorDeclaration 的调用，参数为 env 和 privateEnv。
- 返回
InstantiateAsyncFunctionObject 对AsyncFunctionDeclaration 的调用，参数为 env 和 privateEnv。
8.6.2 运行时语义：绑定初始化
它在以下生成式中逐段定义：
- 让 name 成为
StringValue 的Identifier 。 - 返回 ?
InitializeBoundName (name, value, environment)。
- 返回 ?
InitializeBoundName ("yield" , value, environment)。
- 返回 ?
InitializeBoundName ("await" , value, environment)。
- 执行 ?
RequireObjectCoercible (value)。 - 返回 ?
BindingInitialization ofObjectBindingPattern with arguments value 和 environment。
- 让 iteratorRecord 为 ?
GetIterator (value,sync )。 - 让 result 为
Completion (IteratorBindingInitialization ofArrayBindingPattern with arguments iteratorRecord 和 environment)。 - 如果 iteratorRecord.[[Done]] 为
false ，返回 ?IteratorClose (iteratorRecord, result)。 - 返回 ? result。
- 返回
unused 。
- 执行 ?
PropertyBindingInitialization ofBindingPropertyList with arguments value 和 environment。 - 返回
unused 。
- 让 excludedNames 成为一个新的空
列表 。 - 返回 ?
RestBindingInitialization ofBindingRestProperty with arguments value, environment, 和 excludedNames。
- 让 excludedNames 成为 ?
PropertyBindingInitialization ofBindingPropertyList with arguments value 和 environment。 - 返回 ?
RestBindingInitialization ofBindingRestProperty with arguments value, environment, 和 excludedNames。
8.6.2.1 InitializeBoundName ( name, value, environment )
抽象操作 InitializeBoundName 接受参数 name（字符串），value（一个
- 如果 environment 不是
undefined ，那么- 执行 ! environment.InitializeBinding(name, value）。
- 返回
unused 。
- 否则，
- 让 lhs 等于 ?
ResolveBinding (name）。 - 返回 ?
PutValue (lhs, value）。
- 让 lhs 等于 ?
8.6.3 运行时语义：IteratorBindingInitialization
它通过以下生成式逐段定义：
- 返回
unused 。
- 返回 ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord。
- 如果
Elision 存在，那么- 执行 ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord。
- 执行 ?
- 返回 ?
IteratorBindingInitialization ofBindingRestElement with arguments iteratorRecord 和 environment。
- 执行 ?
IteratorBindingInitialization ofBindingElementList with arguments iteratorRecord 和 environment。 - 返回 ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord。
- 执行 ?
IteratorBindingInitialization ofBindingElementList with arguments iteratorRecord 和 environment。 - 如果
Elision 存在，那么- 执行 ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord。
- 执行 ?
- 返回 ?
IteratorBindingInitialization ofBindingRestElement with arguments iteratorRecord 和 environment。
- 执行 ?
IteratorBindingInitialization ofBindingElementList with arguments iteratorRecord 和 environment。 - 返回 ?
IteratorBindingInitialization ofBindingElisionElement with arguments iteratorRecord 和 environment。
- 执行 ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord。 - 返回 ?
IteratorBindingInitialization ofBindingElement with arguments iteratorRecord 和 environment。
- 设 bindingId 为
字符串值（StringValue） 的绑定标识符（BindingIdentifier） 。 - 设 lhs 为
?
解析绑定（ResolveBinding） (bindingId, environment)。 - 设 v 为
未定义（undefined） 。 - 如果 iteratorRecord 的 [[完成]]（[[Done]]） 为
false ，则：- 设 next 为
?
迭代器步骤值（IteratorStepValue） (iteratorRecord)。 - 如果 next 不是
完成（done） ，则：- 将 v 设为 next。
- 设 next 为
?
- 如果存在
初始化器（Initializer） 且 v 为未定义（undefined） ，则：- 如果
是否匿名函数定义（IsAnonymousFunctionDefinition） (初始化器（Initializer） ) 为true ，则：- 将 v 设为
?
命名评估（NamedEvaluation） (初始化器（Initializer） ，参数为 bindingId)。
- 将 v 设为
?
- 否则：
- 设 defaultValue 为
?
评估（Evaluation） (初始化器（Initializer） )。 - 将 v 设为
?
获取值（GetValue） (defaultValue)。
- 设 defaultValue 为
?
- 如果
- 如果 environment 为
未定义（undefined） ， 则返回 ?放置值（PutValue） (lhs，v)。 - 返回
?
初始化引用绑定（InitializeReferencedBinding） (lhs，v)。
- 设 v 为
未定义（undefined） 。 - 如果 iteratorRecord 的 [[完成]]（[[Done]]） 为
false ，则：- 设 next 为
?
迭代器步骤值（IteratorStepValue） (iteratorRecord)。 - 如果 next 不是
完成（done） ，则：- 将 v 设为 next。
- 设 next 为
?
- 如果存在
初始化器（Initializer） 且 v 为未定义（undefined） ，则：- 设 defaultValue 为
?
评估（Evaluation） (初始化器（Initializer） )。 - 将 v 设为
?
获取值（GetValue） (defaultValue)。
- 设 defaultValue 为
?
- 返回 ?
绑定初始化（BindingInitialization） 的绑定模式（BindingPattern） ，参数为 v 和 environment。
- 设 lhs 为 ?
ResolveBinding (StringValue 的BindingIdentifier , environment)。 - 设 A 为 !
ArrayCreate (0)。 - 设 n 为 0。
- 重复，
- 设 next 为
done 。 - 如果 iteratorRecord 的 [[Done]] 为
false ，则：- 将 next 设为 ?
IteratorStepValue (iteratorRecord)。
- 将 next 设为 ?
- 如果 next 为
done ，则：- 如果 environment 为
undefined ，则返回 ?PutValue (lhs, A)。 - 返回 ?
InitializeReferencedBinding (lhs, A)。
- 如果 environment 为
- 执行 !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), next)。 - 将 n 设为 n + 1。
- 设 next 为
- 设 A 为 !
ArrayCreate (0)。 - 设 n 为 0。
- 重复，
- 设 next 为
done 。 - 如果 iteratorRecord 的 [[Done]] 为
false ，则：- 将 next 设为 ?
IteratorStepValue (iteratorRecord)。
- 将 next 设为 ?
- 如果 next 为
done ，则：- 返回 ?
BindingInitialization ofBindingPattern ，参数为 A 和 environment。
- 返回 ?
- 执行 !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), next)。 - 将 n 设为 n + 1。
- 设 next 为
- 返回
unused 。
- 执行 ?
IteratorBindingInitialization ofFormalParameterList ，参数为 iteratorRecord 和 environment。 - 返回 ?
IteratorBindingInitialization ofFunctionRestParameter ，参数为 iteratorRecord 和 environment。
- 执行 ?
IteratorBindingInitialization ofFormalParameterList ，参数为 iteratorRecord 和 environment。 - 返回 ?
IteratorBindingInitialization ofFormalParameter ，参数为 iteratorRecord 和 environment。
- 令 v 为
undefined 。 断言 ：iteratorRecord.[[Done]] 为false 。- 令 next 为 ?
IteratorStepValue (iteratorRecord)。 - 如果 next 不是
done ，则- 将 v 设置为 next。
- 返回 ?
BindingInitialization ofBindingIdentifier ，参数为 v 和 environment。
- 令 formals 为
ArrowFormalParameters ，它被CoverParenthesizedExpressionAndArrowParameterList 所覆盖。 - 返回 ?
IteratorBindingInitialization of formals，参数为 iteratorRecord 和 environment。
- 令 v 为
undefined 。 断言 ：iteratorRecord.[[Done]] 为false 。- 令 next 为 ?
IteratorStepValue (iteratorRecord)。 - 如果 next 不是
done ，则- 将 v 设置为 next。
- 返回 ?
BindingInitialization ofBindingIdentifier ，参数为 v 和 environment。
8.6.4 静态语义: AssignmentTargetType
语法指导操作
- 如果这个
IdentifierReference 包含在严格模式代码 中，并且Identifier 的StringValue 是"eval" 或"arguments" ，则返回invalid 。 - 返回
simple 。
- 返回
simple 。
- 设 expr 是由
ParenthesizedExpression 所包含 的部分。 - 返回
AssignmentTargetType 的 expr。
- 返回
invalid 。
8.6.5 静态语义：PropName
- 返回
empty .
- 返回
PropName 的PropertyName 。
- 返回
StringValue 的IdentifierName 。
- 返回
SV 的StringLiteral 。
- 让 nbr 为
NumericValue 的NumericLiteral 。 - 返回 !
ToString (nbr)。
- 返回
empty 。
- 返回
PropName 的ClassElementName 。
- 返回
PropName 的ClassElementName 。
- 返回
PropName 的ClassElementName 。
- 返回
empty .
- 返回
empty .
- 返回
PropName 的ClassElementName 。
- 返回
PropName 的ClassElementName 。
- 返回
empty 。
9 可执行代码和执行上下文
9.1 环境记录
环境记录是一种规范类型，用于根据 ECMAScript 代码的词法嵌套结构，定义
每个环境记录都有一个[[OuterEnv]]字段，它要么是
环境记录纯粹是规范机制，不需要对应于 ECMAScript 实现的任何具体产物。ECMAScript 程序不可能直接访问或操作这些值。
9.1.1 环境记录类型层次结构
-
环境记录 （抽象类）
| 方法 | 用途 |
|---|---|
| HasBinding(N) | 确定 |
| CreateMutableBinding(N, D) | 在 |
| CreateImmutableBinding(N, S) | 在 |
| InitializeBinding(N, V) | 设置 |
| SetMutableBinding(N, V, S) | 设置 |
| GetBindingValue(N, S) | 返回 |
| DeleteBinding(N) | 从 |
| HasThisBinding() | 确定this绑定。如果建立了，返回 |
| HasSuperBinding() | 确定super方法绑定。如果建立了，返回 |
| WithBaseObject() | 如果此with语句关联，则返回
with 对象。否则，返回 |
9.1.1.1 声明式环境记录
每个声明式环境记录都与包含变量、常量、let、class、模块、import和/或函数声明的 ECMAScript 程序范围相关联。声明式环境记录绑定其范围内包含的声明所定义的一组标识符。
声明式环境记录的具体规范方法的行为由以下算法定义。
9.1.1.1.1 HasBinding ( N )
- 如果envRec有N的绑定，则返回
true 。 - 返回
false 。
9.1.1.1.2 CreateMutableBinding ( N, D )
断言 ：envRec中不存在N的绑定。- 在envRec中为N创建一个可变绑定，并记录它未初始化。如果D是
true ，则记录新创建的绑定可以通过后续的 DeleteBinding 调用删除。 - 返回
unused 。
9.1.1.1.3 CreateImmutableBinding ( N, S )
断言 ：envRec中不存在N的绑定。- 在envRec中为N创建一个不可变绑定，并记录它未初始化。如果S是
true ，则记录新创建的绑定是严格绑定。 - 返回
unused 。
9.1.1.1.4 InitializeBinding ( N, V )
断言 ：envRec中必须有N的未初始化绑定。- 将envRec中N的绑定值设置为V。
- 记录envRec中N的绑定已被初始化。
- 返回
unused 。
9.1.1.1.5 SetMutableBinding ( N, V, S )
- 如果envRec中没有N的绑定，则
- 如果S是
true ，抛出ReferenceError 异常。 - 执行
! envRec.CreateMutableBinding(N,
true ）。 - 执行 ! envRec.InitializeBinding(N, V）。
- 返回
unused 。
- 如果S是
- 如果envRec中N的绑定是严格绑定，则将S设置为
true 。 - 如果envRec中N的绑定尚未初始化，则
- 抛出
ReferenceError 异常。
- 抛出
- 否则，如果envRec中N的绑定是可变绑定，则
- 将其绑定值更改为V。
- 否则，
断言 ：这是尝试更改不可变绑定的值。- 如果S是
true ，抛出TypeError 异常。
- 返回
unused 。
在步骤
function f() { eval("var x; x = (delete x, 0);"); }9.1.1.1.6 GetBindingValue ( N, S )
断言 ：envRec有N的绑定。- 如果envRec中N的绑定是未初始化绑定，则抛出
ReferenceError 异常。 - 返回当前绑定到envRec中N的值。
9.1.1.1.7 DeleteBinding ( N )
断言 ：envRec有N的绑定。- 如果envRec中N的绑定不能被删除，则返回
false 。 - 从envRec中移除N的绑定。
- 返回
true 。
9.1.1.1.8 HasThisBinding ( )
- 返回
false 。
9.1.1.1.9 HasSuperBinding ( )
- 返回
false 。
9.1.1.1.10 WithBaseObject ( )
- 返回
undefined 。
9.1.1.2 对象环境记录
每个对象环境记录都与一个称为绑定对象的对象相关联。对象环境记录绑定一组字符串标识符名称，这些名称直接对应于其绑定对象的属性名称。
为with语句创建的对象环境记录（
对象环境记录具有
对象环境记录的具体规范方法的行为由以下算法定义。
9.1.1.2.1 HasBinding ( N )
- 让bindingObject成为envRec的[[BindingObject]]。
- 让foundBinding为?
HasProperty (bindingObject, N）。 - 如果foundBinding为
false ，返回false 。 - 如果envRec的[[IsWithEnvironment]]为
false ，返回true 。 - 让unscopables为?
Get (bindingObject,@@unscopables ）。 - 如果unscopables是一个
对象 ，则 - 返回
true 。
9.1.1.2.2 CreateMutableBinding ( N, D )
- 让bindingObject成为envRec的[[BindingObject]]。
- 执行?
DefinePropertyOrThrow (bindingObject, N, PropertyDescriptor { [[Value]]:undefined , [[Writable]]:true , [[Enumerable]]:true , [[Configurable]]: D }）。 - 返回
unused 。
通常情况下，envRec不会有N的绑定，但如果有，
9.1.1.2.3 CreateImmutableBinding ( N, S )
9.1.1.2.4 InitializeBinding ( N, V )
- 执行? envRec.SetMutableBinding(N, V,
false ）。 - 返回
unused 。
9.1.1.2.5 SetMutableBinding ( N, V, S )
- 让bindingObject成为envRec的[[BindingObject]]。
- 让stillExists为?
HasProperty (bindingObject, N）。 - 如果stillExists为
false 且S为true ，抛出ReferenceError 异常。 - 执行?
Set (bindingObject, N, V, S）。 - 返回
unused 。
9.1.1.2.6 GetBindingValue ( N, S )
- 让bindingObject成为envRec的[[BindingObject]]。
- 让value为?
HasProperty (bindingObject, N）。 - 如果value为
false ，则- 如果S为
false ，返回undefined ；否则抛出ReferenceError 异常。
- 如果S为
- 返回?
Get (bindingObject, N）。
9.1.1.2.7 DeleteBinding ( N )
- 让bindingObject成为envRec的[[BindingObject]]。
- 返回? bindingObject.[[Delete]](N）。
9.1.1.2.8 HasThisBinding ( )
- 返回
false 。
this绑定。
9.1.1.2.9 HasSuperBinding ( )
- 返回
false 。
super绑定。
9.1.1.2.10 WithBaseObject ( )
- 如果envRec的[[IsWithEnvironment]]为
true ，返回envRec的[[BindingObject]]。 - 否则，返回
undefined 。
9.1.1.3 函数环境记录
函数环境记录 是一种
this绑定。如果函数不是一个super，则其函数环境记录还包含用于在函数内部执行super方法调用的状态。
函数环境记录具有
| 字段名称 | 值 | 含义 |
|---|---|---|
| [[ThisValue]] |
一个 |
这是该函数调用中使用的 |
| [[ThisBindingStatus]] |
|
如果值是 |
| [[FunctionObject]] |
一个ECMAScript |
导致创建此 |
| [[NewTarget]] |
一个对象或 |
如果此 |
函数环境记录支持
函数环境记录附加具体方法的行为由以下算法定义：
9.1.1.3.1 BindThisValue ( V )
函数环境记录
断言 : envRec.[[ThisBindingStatus]]不是lexical 。- 如果envRec.[[ThisBindingStatus]]是
initialized ，抛出ReferenceError 异常。 - 将envRec.[[ThisValue]]设置为V。
- 将envRec.[[ThisBindingStatus]]设置为
initialized 。 - 返回V。
9.1.1.3.2 HasThisBinding ( )
函数环境记录
- 如果envRec.[[ThisBindingStatus]]是
lexical ，返回false ； 否则，返回true 。
9.1.1.3.3 HasSuperBinding ( )
函数环境记录
- 如果envRec.[[ThisBindingStatus]]是
lexical ，返回false 。 - 如果envRec.[[FunctionObject]].[[HomeObject]]是
undefined ，返回false ； 否则，返回true 。
9.1.1.3.4 GetThisBinding ( )
函数环境记录
断言 : envRec.[[ThisBindingStatus]]不是lexical 。- 如果envRec.[[ThisBindingStatus]]是
uninitialized ，抛出ReferenceError 异常。 - 返回envRec.[[ThisValue]]。
9.1.1.3.5 GetSuperBase ( )
函数环境记录
9.1.1.4 全局环境记录
全局环境记录用于表示所有在同一个
全局环境记录在逻辑上是一个单一的记录，但它被指定为一个复合体，封装了一个
属性可以直接在
全局环境记录具有
| 字段名称 | 值 | 含义 |
|---|---|---|
| [[ObjectRecord]] |
一个 |
绑定对象是 |
| [[GlobalThisValue]] | 一个对象 |
全局作用域中this返回的值。 |
| [[DeclarativeRecord]] |
一个 |
|
| [[VarNames]] |
一个 |
在相关 |
| 方法 | 目的 |
|---|---|
| GetThisBinding() |
返回此this绑定的值。
|
| HasVarDeclaration (N) |
确定参数标识符是否在此 |
| HasLexicalDeclaration (N) |
确定参数标识符是否在此 |
| HasRestrictedGlobalProperty (N) |
确定参数是否为 |
| CanDeclareGlobalVar (N) | 确定是否可以成功调用相应的CreateGlobalVarBinding方法，并为相同的参数N声明全局变量。 |
| CanDeclareGlobalFunction (N) | 确定是否可以成功调用相应的CreateGlobalFunctionBinding方法，并为相同的参数N声明全局函数。 |
| CreateGlobalVarBinding(N, D) |
用于在[[ObjectRecord]]组件中创建并初始化一个全局var绑定，
该绑定的初始值为var的属性值。
字符串值N是绑定的名称。如果D为 |
| CreateGlobalFunctionBinding(N, V, D) |
在[[ObjectRecord]]组件中创建并初始化一个全局function绑定。
绑定将是可变绑定。相应的function的属性值。
字符串值N是绑定的名称。V是初始化值。
如果布尔参数D为 |
具体规范方法的行为定义如下算法。
9.1.1.4.1 HasBinding ( N )
全局环境记录envRec的HasBinding具体方法接受参数N（字符串），返回一个
- 设DclRec为envRec的[[DeclarativeRecord]]。
- 如果! DclRec.HasBinding(N)为
true ，返回true 。 - 设ObjRec为envRec的[[ObjectRecord]]。
- 返回? ObjRec.HasBinding(N)。
9.1.1.4.2 CreateMutableBinding ( N, D )
全局环境记录envRec的CreateMutableBinding具体方法接受参数N（字符串）和D（布尔值），返回一个
- 设DclRec为envRec的[[DeclarativeRecord]]。
- 如果! DclRec.HasBinding(N)为
true ，抛出类型错误 异常。 - 返回 ! DclRec.CreateMutableBinding(N, D)。
9.1.1.4.3 CreateImmutableBinding ( N, S )
全局环境记录envRec的CreateImmutableBinding具体方法接受参数N（字符串）和S（布尔值），返回一个
- 设DclRec为envRec的[[DeclarativeRecord]]。
- 如果! DclRec.HasBinding(N)为
true ，抛出类型错误 异常。 - 返回 ! DclRec.CreateImmutableBinding(N, S)。
9.1.1.4.4 InitializeBinding ( N, V )
全局环境记录envRec的InitializeBinding具体方法接受参数N（字符串）和V（
9.1.1.4.5 SetMutableBinding ( N, V, S )
全局环境记录envRec的SetMutableBinding具体方法接受参数N（字符串）、V（
- 设DclRec为envRec的[[DeclarativeRecord]]。
- 如果! DclRec.HasBinding(N)为
true ，则- 返回 ? DclRec.SetMutableBinding(N, V, S)。
- 设ObjRec为envRec的[[ObjectRecord]]。
- 返回? ObjRec.SetMutableBinding(N, V, S)。
9.1.1.4.6 GetBindingValue ( N, S )
全局环境记录envRec的GetBindingValue具体方法接受参数N（字符串）和S（布尔值），返回一个
- 设DclRec为envRec的[[DeclarativeRecord]]。
- 如果! DclRec.HasBinding(N)为
true ，则- 返回 ? DclRec.GetBindingValue(N, S)。
- 设ObjRec为envRec的[[ObjectRecord]]。
- 返回? ObjRec.GetBindingValue(N, S)。
9.1.1.4.7 DeleteBinding ( N )
全局环境记录envRec的DeleteBinding具体方法接受参数N（字符串），返回一个
- 设DclRec为envRec的[[DeclarativeRecord]]。
- 如果! DclRec.HasBinding(N)为
true ，则- 返回 ! DclRec.DeleteBinding(N)。
- 设ObjRec为envRec的[[ObjectRecord]]。
- 设globalObject为ObjRec的[[BindingObject]]。
- 设existingProp为?
HasOwnProperty (globalObject, N)。 - 如果existingProp为
true ，则- 设status为? ObjRec.DeleteBinding(N)。
- 如果status为
true ，并且envRec的[[VarNames]]包含N，则- 从envRec的[[VarNames]]中删除N。
- 返回status。
- 返回
true 。
9.1.1.4.8 HasThisBinding ( )
全局环境记录envRec的HasThisBinding具体方法不接受参数，返回
- 返回
true 。
this绑定。
9.1.1.4.9 HasSuperBinding ( )
全局环境记录envRec的HasSuperBinding具体方法不接受参数，返回
- 返回
false 。
super绑定。
9.1.1.4.10 WithBaseObject ( )
全局环境记录envRec的WithBaseObject具体方法不接受参数，返回
- 返回
undefined 。
9.1.1.4.11 GetThisBinding ( )
全局环境记录envRec的GetThisBinding具体方法不接受参数，返回一个
- 返回envRec的[[GlobalThisValue]]。
9.1.1.4.12 HasVarDeclaration ( N )
全局环境记录envRec的HasVarDeclaration具体方法接受参数N（字符串），返回一个布尔值。它确定参数标识符是否在此记录中具有通过
- 设varDeclaredNames为envRec的[[VarNames]]。
- 如果varDeclaredNames包含N，返回
true 。 - 返回
false 。
9.1.1.4.13 HasLexicalDeclaration ( N )
全局环境记录envRec的HasLexicalDeclaration具体方法接受参数N（字符串），返回一个布尔值。它确定参数标识符是否在此记录中具有通过词法声明（如
- 设DclRec为envRec的[[DeclarativeRecord]]。
- 返回! DclRec.HasBinding(N)。
9.1.1.4.14 HasRestrictedGlobalProperty ( N )
全局环境记录envRec的HasRestrictedGlobalProperty具体方法接受参数N（字符串），返回一个
- 设ObjRec为envRec的[[ObjectRecord]]。
- 设globalObject为ObjRec的[[BindingObject]]。
- 设existingProp为? globalObject.[[GetOwnProperty]](N)。
- 如果existingProp为
未定义 ， 返回false 。 - 如果existingProp的[[Configurable]]为
true ，返回false 。 - 返回
true 。
9.1.1.4.15 CanDeclareGlobalVar ( N )
全局环境记录envRec的CanDeclareGlobalVar具体方法接受参数N（字符串），返回一个
- 设ObjRec为envRec的[[ObjectRecord]]。
- 设globalObject为ObjRec的[[BindingObject]]。
- 设hasProperty为?
HasOwnProperty (globalObject, N)。 - 如果hasProperty为
true ，返回true 。 - 返回?
IsExtensible (globalObject)。
9.1.1.4.16 CanDeclareGlobalFunction ( N )
全局环境记录envRec的CanDeclareGlobalFunction具体方法接受参数N（字符串），返回一个
- 设ObjRec为envRec的[[ObjectRecord]]。
- 设globalObject为ObjRec的[[BindingObject]]。
- 设existingProp为? globalObject.[[GetOwnProperty]](N)。
- 如果existingProp为
未定义 ， 返回?IsExtensible (globalObject)。 - 如果existingProp的[[Configurable]]为
true ，返回true 。 - 如果
IsDataDescriptor (existingProp) 为true ，且existingProp具有属性值{ [[Writable]]:true , [[Enumerable]]:true }，返回true 。 - 返回
false 。
9.1.1.4.17 CreateGlobalVarBinding ( N, D )
全局环境记录envRec的CreateGlobalVarBinding具体方法接受参数N（字符串）和D（布尔值），返回一个
- 设ObjRec为envRec的[[ObjectRecord]]。
- 设globalObject为ObjRec的[[BindingObject]]。
- 设hasProperty为?
HasOwnProperty (globalObject, N)。 - 设extensible为?
IsExtensible (globalObject)。 - 如果hasProperty为
false 并且extensible为true ，则- 执行? ObjRec.CreateMutableBinding(N, D)。
- 执行? ObjRec.InitializeBinding(N,
未定义 )。
- 如果envRec的[[VarNames]]
不包含N，则
- 将N追加到envRec的[[VarNames]]中。
- 返回
未使用 。
9.1.1.4.18 CreateGlobalFunctionBinding ( N, V, D )
全局环境记录envRec的CreateGlobalFunctionBinding具体方法接受参数N（字符串）、V（
- 设ObjRec为envRec的[[ObjectRecord]]。
- 设globalObject为ObjRec的[[BindingObject]]。
- 设existingProp为? globalObject.[[GetOwnProperty]](N)。
- 如果existingProp为
未定义 或existingProp的[[Configurable]]为true ，则- 设desc为属性描述符{ [[Value]]:
V, [[Writable]]:
true , [[Enumerable]]:true , [[Configurable]]: D }.
- 设desc为属性描述符{ [[Value]]:
V, [[Writable]]:
- 否则，
- 设desc为属性描述符{ [[Value]]: V }。
- 执行?
DefinePropertyOrThrow (globalObject, N, desc)。 - 执行
?
Set (globalObject, N, V,false )。 - 如果envRec的[[VarNames]]
不包含N，则
- 将N追加到envRec的[[VarNames]]中。
- 返回
未使用 。
9.1.1.5 模块环境记录
模块环境记录 是一种
模块环境记录支持所有在
模块环境记录的附加具体规范方法的行为由以下算法定义：
9.1.1.5.1 GetBindingValue ( N, S )
模块环境记录的 GetBindingValue 具体方法 envRec 接受参数 N（字符串）和 S（布尔值），返回一个包含
ECMAScript 语言值的正常完成记录或抛出完成记录。它返回其绑定标识符 N 的值。但是，如果绑定是间接绑定，则返回目标绑定的值。如果绑定存在但未初始化，则抛出
S 将始终为
9.1.1.5.2 DeleteBinding ( N )
模块环境记录的 DeleteBinding 具体方法在本规范中从未使用。
9.1.1.5.3 HasThisBinding ( )
模块环境记录的 HasThisBinding 具体方法 envRec 不接受任何参数并返回
- 返回
true 。
模块环境记录始终提供 this 绑定。
9.1.1.5.4 GetThisBinding ( )
模块环境记录的 GetThisBinding 具体方法 envRec 不接受任何参数并返回
- 返回
undefined 。
9.1.1.5.5 CreateImportBinding ( N, M, N2 )
模块环境记录的 CreateImportBinding 具体方法 envRec 接受参数 N（字符串）、M（模块记录）和 N2（字符串），并返回
9.1.2 环境记录操作
9.1.2.1 GetIdentifierReference ( env, name, strict )
抽象操作 GetIdentifierReference 接受参数 env（一个
- 如果 env 是
null ，则- 返回
引用记录 { [[Base]]:unresolvable , [[ReferencedName]]: name, [[Strict]]: strict, [[ThisValue]]:empty }。
- 返回
- 设 exists 为 ? env.HasBinding(name)。
- 如果 exists 为
true ，则- 返回
引用记录 { [[Base]]: env, [[ReferencedName]]: name, [[Strict]]: strict, [[ThisValue]]:empty }。
- 返回
- 否则，
- 设 outer 为 env.[[OuterEnv]]。
- 返回 ?
GetIdentifierReference (outer, name, strict)。
9.1.2.2 NewDeclarativeEnvironment ( E )
抽象操作 NewDeclarativeEnvironment 接受参数 E（一个
- 设 env 为一个新的
声明环境记录 ，其中不包含任何绑定。 - 将 env.[[OuterEnv]] 设置为 E。
- 返回 env。
9.1.2.3 NewObjectEnvironment ( O, W, E )
抽象操作 NewObjectEnvironment 接受参数 O（一个对象）、W（布尔值）和 E（一个
- 设 env 为一个新的
对象环境记录 。 - 将 env.[[BindingObject]] 设置为 O。
- 将 env.[[IsWithEnvironment]] 设置为 W。
- 将 env.[[OuterEnv]] 设置为 E。
- 返回 env。
9.1.2.4 NewFunctionEnvironment ( F, newTarget )
抽象操作 NewFunctionEnvironment 接受参数 F（一个 ECMAScript
- 设 env 为一个新的
函数环境记录 ，其中不包含任何绑定。 - 将 env.[[FunctionObject]] 设置为 F。
- 如果 F.[[ThisMode]] 为
lexical ，将 env.[[ThisBindingStatus]] 设置为lexical 。 - 否则，将 env.[[ThisBindingStatus]] 设置为
uninitialized 。 - 将 env.[[NewTarget]] 设置为 newTarget。
- 将 env.[[OuterEnv]] 设置为 F.[[Environment]]。
- 返回 env。
9.1.2.5 NewGlobalEnvironment ( G, thisValue )
抽象操作 NewGlobalEnvironment 接受参数 G（一个对象）和 thisValue（一个对象），返回一个
- 设 objRec 为
NewObjectEnvironment (G,false ,null )。 - 设 dclRec 为
NewDeclarativeEnvironment (null )。 - 设 env 为一个新的
全局环境记录 。 - 将 env.[[ObjectRecord]] 设置为 objRec。
- 将 env.[[GlobalThisValue]] 设置为 thisValue。
- 将 env.[[DeclarativeRecord]] 设置为 dclRec。
- 将 env.[[VarNames]] 设置为一个新的空
列表 。 - 将 env.[[OuterEnv]] 设置为
null 。 - 返回 env。
9.1.2.6 NewModuleEnvironment ( E )
抽象操作 NewModuleEnvironment 接受参数 E（一个
- 设 env 为一个新的
模块环境记录 ，其中不包含任何绑定。 - 将 env.[[OuterEnv]] 设置为 E。
- 返回 env。
9.2 私有环境记录
私有环境记录 是一种用于根据
ECMAScript 代码中的
9.2.1 私有环境记录操作
9.2.1.1 NewPrivateEnvironment ( outerPrivEnv )
抽象操作 NewPrivateEnvironment 接受参数 outerPrivEnv（一个
9.2.1.2 ResolvePrivateIdentifier ( privEnv, identifier )
抽象操作 ResolvePrivateIdentifier 接受参数 privEnv（一个
- 设 names 为 privEnv.[[Names]]。
-
对于 names 中的每个
私有名称 pn， 执行以下步骤：-
如果 pn.[[Description]] 是
identifier，则：
- 返回 pn。
-
如果 pn.[[Description]] 是
identifier，则：
- 设 outerPrivEnv 为 privEnv.[[OuterPrivateEnvironment]]。
-
断言 ： outerPrivEnv 不为null 。 -
返回
ResolvePrivateIdentifier ( outerPrivEnv, identifier)。
9.3 范围（Realms）
在评估之前，所有 ECMAScript 代码都必须与一个 范围 相关联。从概念上讲，一个
本规范中以 范围记录 表示
| 字段名称 | 值 | 含义 |
|---|---|---|
| [[AgentSignifier]] | 一个 |
拥有此 |
| [[Intrinsics]] | 一个 |
与此 |
| [[GlobalObject]] | 一个对象或 |
此 |
| [[GlobalEnv]] | 一个 |
此 |
| [[TemplateMap]] | 一个 |
模板对象在每个 一旦
|
| [[LoadedModules]] | 一个 |
从此 正如在
import() 表达式时使用。
|
| [[HostDefined]] | 任何（默认值为 |
为 |
9.3.1 创建范围（CreateRealm） ( )
抽象操作 CreateRealm 不接受任何参数并返回一个
- 设 realmRec 为一个新的
范围记录 。 - 执行
CreateIntrinsics (realmRec)。 - 将 realmRec.[[AgentSignifier]]
设置为
AgentSignifier ()。 - 将 realmRec.[[GlobalObject]] 设置为
undefined 。 - 将 realmRec.[[GlobalEnv]] 设置为
undefined 。 - 将 realmRec.[[TemplateMap]]
设置为一个新的空
列表 。 - 返回 realmRec。
9.3.2 创建内置对象（CreateIntrinsics） ( realmRec )
抽象操作 CreateIntrinsics 接受参数 realmRec（一个
- 将 realmRec.[[Intrinsics]]
设置为一个新的
记录 。 -
使用
表 6 中列出的值设置 realmRec.[[Intrinsics]] 的字段。这些字段名称是表的第一列中列出的名称。每个字段的值是一个新的对象值，按照规范中的定义完全递归地填充属性值。这些对象的创建顺序必须避免对尚未创建的对象的依赖。 - 执行
AddRestrictedFunctionProperties (realmRec.[[Intrinsics]].[[%Function.prototype% ]], realmRec)。 - 返回
unused 。
9.3.3 设置范围全局对象（SetRealmGlobalObject） ( realmRec, globalObj, thisValue )
抽象操作 SetRealmGlobalObject 接受参数 realmRec（一个
-
如果 globalObj 是
undefined ，则：- 设 intrinsics 为 realmRec.[[Intrinsics]]。
- 将 globalObj 设置为
OrdinaryObjectCreate (intrinsics.[[%Object.prototype% ]])。
断言 ：globalObj 是一个对象 。- 如果 thisValue 是
undefined ，则将 thisValue 设置为 globalObj。 - 将 realmRec.[[GlobalObject]] 设置为 globalObj。
- 设 newGlobalEnv 为
NewGlobalEnvironment (globalObj, thisValue)。 - 将 realmRec.[[GlobalEnv]] 设置为 newGlobalEnv。
- 返回
unused 。
9.3.4 设置默认全局绑定（SetDefaultGlobalBindings） ( realmRec )
抽象操作 SetDefaultGlobalBindings 接受参数 realmRec（一个
9.4 执行上下文（Execution Contexts）
执行上下文 是一个规范设备，用于跟踪 ECMAScript 实现对代码的运行时评估。在任何时候，每个
执行上下文堆栈
用于跟踪执行上下文。
执行上下文包含所有跟踪其关联代码执行进度的必要实现特定状态。每个执行上下文至少有
ECMAScript 代码执行上下文 具有
执行上下文的词法环境和变量环境组件始终是
表示生成器评估的执行上下文具有
| 组件 | 目的 |
|---|---|
| 生成器 | 此 |
在大多数情况下，仅由此规范中的算法直接操作
执行上下文纯粹是一个规范机制，不需要对应于 ECMAScript 实现的任何特定制品。ECMAScript 代码不可能直接访问或观察到执行上下文。
9.4.1 GetActiveScriptOrModule ( )
抽象操作 GetActiveScriptOrModule 不接受参数，并返回
9.4.2 ResolveBinding ( name [ , env ] )
抽象操作 ResolveBinding 接受参数 name（一个字符串）和可选参数 env（一个
- 如果未提供 env 或 env 为
undefined ，则- 将 env 设置为
正在运行的执行上下文 的词法环境。
- 将 env 设置为
断言 ：env 是一个环境记录 。- 如果正在评估的语法生成的
源文本匹配 包含在严格模式代码 中，则将 strict 设置为true ；否则将 strict 设置为false 。 - 返回 ?
GetIdentifierReference (env, name, strict)。
ResolveBinding 的结果始终是一个
9.4.3 GetThisEnvironment ( )
抽象操作 GetThisEnvironment 不接受参数，并返回一个 this
绑定的
- 将 env 设置为
正在运行的执行上下文 的词法环境。 - 重复以下步骤，直到条件不成立为止：
- 让 exists 为 env.HasThisBinding()。
- 如果 exists 为
true ，则返回 env。 - 将 outer 设置为 env.[[OuterEnv]]。
断言 ：outer 不是null 。- 将 env 设置为 outer。
步骤 this 绑定的全局环境结束。
9.4.4 ResolveThisBinding ( )
抽象操作 ResolveThisBinding 不接受参数，并返回 this 的绑定。调用时执行以下步骤：
- 设 envRec 为
GetThisEnvironment ()。 - 返回 ? envRec.GetThisBinding()。
9.4.5 GetNewTarget ( )
抽象操作 GetNewTarget 不接受参数，并返回一个对象或
- 设 envRec 为
GetThisEnvironment ()。 断言 ：envRec 具有 [[NewTarget]] 字段。- 返回 envRec.[[NewTarget]]。
9.4.6 GetGlobalObject ( )
抽象操作 GetGlobalObject 不接受参数并返回一个对象。它返回由当前
- 设 currentRealm 为
当前范围记录 。 - 返回 currentRealm.[[GlobalObject]]。
9.5 Jobs and Host Operations to Enqueue Jobs
作业是一个无参数的
- 在将来的某个时间，当为其调度作业的
代理 中没有正在运行的上下文，并且该代理 的执行上下文堆栈 为空时，实现必须： - 在任何时间点，一个
代理 中只能有一个作业 正在积极评估。 - 一旦一个
代理 中的作业 的评估开始，必须在完成之前运行完毕，然后才能在该代理 中开始评估任何其他作业 。 抽象闭包 必须返回正常完成 ，实现其自己的错误处理。
在任何特定时间，如果以下所有条件都为真，则scriptOrModule（一个
GetActiveScriptOrModule 是scriptOrModule。- 如果scriptOrModule是一个
脚本记录 或一个模块记录 ，则设ec为执行上下文 堆栈上的最顶层的执行上下文 ，其ScriptOrModule组件是scriptOrModule。ec的范围 组件是scriptOrModule的[[Realm]]。
在任何特定时间，如果以下所有条件都为真，则执行准备好评估 ECMAScript 代码：
特定种类的
9.5.1 作业回调记录
作业回调记录是一个
WHATWG HTML 规范（https://html.spec.whatwg.org/）例如，使用宿主定义的值传播 Promise 回调的现有设置对象。
作业回调记录具有
9.5.2 HostMakeJobCallback ( callback )
HostMakeJobCallback 的实现必须符合以下要求：
- 它必须返回一个作业回调记录，其[[Callback]]字段是callback。
HostMakeJobCallback 的默认实现在调用时执行以下步骤：
- 返回作业回调记录 { [[Callback]]:
callback，[[HostDefined]]:
empty }。
不是网络浏览器的 ECMAScript 宿主必须使用 HostMakeJobCallback 的默认实现。
这在将回调传递给负责其最终调度和运行的函数时调用。例如，promise.then(thenAction)在调用Promise.prototype.then时调用
MakeJobCallback
在调用Promise.prototype.then时调用 MakeJobCallback，而不是在调度反应作业时。
9.5.3 HostCallJobCallback ( jobCallback, V, argumentsList )
HostCallJobCallback 的实现必须符合以下要求：
- 它必须执行并返回
调用 (jobCallback.[[Callback]]，V，argumentsList)的结果。
此要求意味着宿主不能更改本规范中定义的函数对象的[[Call]]行为。
HostCallJobCallback 的默认实现在调用时执行以下步骤：
断言 ：IsCallable (jobCallback.[[Callback]]) 为true 。- 返回？
调用 (jobCallback.[[Callback]]，V，argumentsList)的结果。
不是网络浏览器的 ECMAScript 宿主必须使用 HostCallJobCallback 的默认实现。
9.5.4 HostEnqueueGenericJob ( job, realm )
HostEnqueueGenericJob 的实现必须符合
9.5.5 HostEnqueuePromiseJob ( job, realm )
HostEnqueuePromiseJob 的实现必须符合
- 如果realm不是
null ，每次调用job时，实现必须执行实现定义的 步骤，以确保在调用job时执行准备评估 ECMAScript 代码 。 - 在调用 HostEnqueuePromiseJob 时，scriptOrModule为
GetActiveScriptOrModule 。如果realm不是null ，每次调用job时，实现必须执行实现定义的 步骤，以确保scriptOrModule在调用job时是活动脚本或模块 。 - 作业必须按照 HostEnqueuePromiseJob 调用的顺序运行。
通过
9.5.6 HostEnqueueTimeoutJob ( timeoutJob, realm, milliseconds )
HostEnqueueTimeoutJob 的实现必须符合
9.6 InitializeHostDefinedRealm ( )
抽象操作 InitializeHostDefinedRealm 不接受任何参数，返回一个包含
- 让 realm 为
CreateRealm () 的结果。 - 让 newContext 为一个新的
执行上下文 。 - 将 newContext 的 Function 设置为
null 。 - 将 newContext 的
Realm 设置为 realm。 - 将 newContext 的 ScriptOrModule 设置为
null 。 - 将 newContext 推入
执行上下文栈 ；newContext 现在是运行中的执行上下文 。 - 如果
宿主 需要使用一个特殊对象 作为 realm 的全局对象 ，则让 global 为以宿主定义 的方式创建的此类对象。否则，让 global 为undefined ，表示应创建一个普通对象 作为全局对象 。 - 如果
宿主 需要this绑定在 realm 的全局作用域中返回一个不同于全局对象 的对象，则让 thisValue 为以宿主定义 的方式创建的此类对象。否则，让 thisValue 为undefined ，表示 realm 的全局this绑定应为全局对象 。 - 执行
SetRealmGlobalObject (realm, global, thisValue)。 - 让 globalObj 为 ?
SetDefaultGlobalBindings (realm) 的结果。 - 在 globalObj 上创建任何
宿主定义 的全局对象 属性。 - 返回
unused 。
9.7 Agents
一个代理包括一组ECMAScript
一个
一些网络浏览器会在多个不相关的浏览器窗口标签页之间共享单个
当一个
一个代理标识符是一个全局唯一的、不透明的值，用于标识一个
| 字段名 | 值 | 含义 |
|---|---|---|
| [[LittleEndian]] | 布尔值 | 在算法 |
| [[CanBlock]] | 布尔值 | 确定 |
| [[Signifier]] | 一个 |
唯一标识其 |
| [[IsLockFree1]] | 布尔值 | 如果对一个字节大小值的原子操作是无锁的，则为 |
| [[IsLockFree2]] | 布尔值 | 如果对两字节大小值的原子操作是无锁的，则为 |
| [[IsLockFree8]] | 布尔值 | 如果对八字节大小值的原子操作是无锁的，则为 |
| [[CandidateExecution]] | 一个 |
参见 |
| [[KeptAlive]] | 一个 |
最初是一个新的空 |
一旦[[Signifier]]、[[IsLockFree1]]和[[IsLockFree2]]的值被任何
[[IsLockFree1]]和[[IsLockFree2]]的值不一定由硬件决定，还可能反映出可能随时间和不同ECMAScript实现而变化的实现选择。
没有[[IsLockFree4]]字段：四字节原子操作总是无锁的。
实际上，如果一个原子操作的实现使用了任何类型的锁，则该操作就不是无锁的。无锁不意味着无等待：没有关于完成无锁原子操作需要多少机器步骤的上限。
原子访问大小为n是无锁的，并不意味着对非原子访问大小为n的访问有任何暗示，特别是，非原子访问仍可能作为一系列单独的内存访问执行。详见
一个
9.7.1 AgentSignifier ( )
抽象操作 AgentSignifier 不接受任何参数，并返回一个
9.7.2 AgentCanSuspend ( )
抽象操作 AgentCanSuspend 不接受任何参数，并返回一个布尔值。调用时，它执行以下步骤：
在某些环境中，允许给定
9.8 代理集群
一个代理集群是可以通过操作共享内存进行通信的
每个
集群中的所有
如果一个代理集群中的不同
集群中的所有
集群中的所有
嵌入环境可以在不通知或合作代理的情况下停用（停止前进进程）或激活（恢复前进进程）一个
嵌入环境可以在不通知或合作集群中其他
每个以下的规范值及从它们递归可达的值，只属于一个代理集群。
在集群中任何
代理集群是一个规范机制，不必对应于ECMAScript实现的任何特定工件。
9.9 前进进度
对于一个
当
实现必须确保：
9.10 WeakRef 和 FinalizationRegistry 目标的处理模型
9.10.1 目标
本规范不保证任何对象或符号将被垃圾回收。对于那些不是
-
当调用
WeakRef.prototype.deref时，如果未返回undefined ，则被引用对象保持存活，以便随后的同步访问也返回相同的值。当使用ClearKeptObjects 抽象操作进行同步工作时，此列表会被重置。 -
当与
FinalizationRegistry 注册的对象或符号变得不可达时，可能会在同步 ECMAScript 执行完成后调用FinalizationRegistry 的清理回调。清理通过CleanupFinalizationRegistry 抽象操作进行。
这些操作（
一些 ECMAScript 实现包括在后台运行的垃圾回收器实现，包括 ECMAScript 空闲时。让
9.10.2 存活性
对于某些对象和/或符号的集合S，相对于S的假设的 WeakRef-oblivious执行是指抽象操作
在评估过程中，如果对象和/或符号的集合S满足以下任一条件，则被认为是存活的：
对象或符号在字段、内部槽或属性中的存在并不意味着该值是存活的。例如，如果问题中的值从未传递回程序，则无法观察到它。
这是 WeakMap 中的键、WeakSet 的成员以及[[WeakRefTarget]]和[[UnregisterToken]]字段在
上述定义意味着，如果 WeakMap 中的键不是存活的，则其对应的值也不一定是存活的。
9.10.3 执行
在任何时候，如果对象和/或符号的集合S不是
- 对于S的每个元素value，执行以下操作
- 对于每个
WeakRef ，如果ref的[[WeakRefTarget]]是value，则执行以下操作- 将ref的[[WeakRefTarget]]设置为
empty 。
- 将ref的[[WeakRefTarget]]设置为
- 对于每个
FinalizationRegistry ，如果fg的[[Cells]]包含一个记录 ，其中cell的[[WeakRefTarget]]是value，则执行以下操作- 将cell的[[WeakRefTarget]]设置为
empty 。 - 可选地，执行
HostEnqueueFinalizationRegistryCleanupJob (fg)。
- 将cell的[[WeakRefTarget]]设置为
- 对于每个 WeakMapmap，如果map的[[WeakMapData]]包含一个
记录 ，其中r的[[Key]]是value，则执行以下操作- 将r的[[Key]]设置为
empty 。 - 将r的[[Value]]设置为
empty 。
- 将r的[[Key]]设置为
- 对于每个 WeakSetset，如果set的[[WeakSetData]]包含value，则执行以下操作
- 用值为
empty 的元素替换set的[[WeakSetData]]中值为value的元素。
- 用值为
- 对于每个
结合存活性的定义，本条款规定了实现可以应用的关于
有可能在不观察对象身份的情况下访问对象。允许对非逃逸对象的属性进行死变量消除和标量替换等优化，因此这些优化可以可观察地清空指向这些对象的
另一方面，如果可以观察到对象的身份，并且该对象位于
由于调用
9.10.4 宿主钩子
9.10.4.1 HostEnqueueFinalizationRegistryCleanupJob (finalizationRegistry)
让cleanupJob成为一个新的
- 令cleanupResult为
完成 (CleanupFinalizationRegistry (finalizationRegistry))。 - 如果cleanupResult是一个
异常完成 ，执行任何宿主定义的 步骤来报告错误。 - 返回
unused 。
HostEnqueueFinalizationRegistryCleanupJob 的实现会安排在将来的某个时间执行cleanupJob，如果可能的话。它还必须符合
9.11 ClearKeptObjects ( )
抽象操作 ClearKeptObjects 不接受任何参数并返回
9.12 AddToKeptObjects ( value )
抽象操作 AddToKeptObjects 接受参数 value（一个对象或符号）并返回
9.13 CleanupFinalizationRegistry ( finalizationRegistry )
抽象操作 CleanupFinalizationRegistry 接受参数 finalizationRegistry（一个
断言 ：finalizationRegistry 具有 [[Cells]] 和 [[CleanupCallback]] 内部槽。- 让 callback 为 finalizationRegistry.[[CleanupCallback]]。
- 当 finalizationRegistry.[[Cells]]
包含一个
记录 cell，其 [[WeakRefTarget]] 为empty 时，实现可以执行以下步骤：- 选择任意这样的 cell。
- 从 finalizationRegistry.[[Cells]] 中移除 cell。
- 执行 ?
HostCallJobCallback (callback,undefined , « cell.[[HeldValue]] »)。
- 返回
unused 。
9.14 CanBeHeldWeakly ( v )
抽象操作 CanBeHeldWeakly 接受参数 v（一个
- 如果 v
是一个对象 ，返回true 。 - 如果 v
是一个符号 ，并且KeyForSymbol (v) 是undefined ，返回true 。 - 返回
false 。
没有
10 普通对象和奇异对象的行为
10.1 普通对象的内部方法和内部槽
所有的
每个
在以下算法描述中，假设 O 是一个
每个
10.1.1 [[GetPrototypeOf]] ( )
[[GetPrototypeOf]] 内部方法用于一个
- 返回
OrdinaryGetPrototypeOf (O)。
10.1.1.1 OrdinaryGetPrototypeOf ( O )
抽象操作 OrdinaryGetPrototypeOf 接受一个参数 O（一个对象），并返回一个对象或
- 返回 O.[[Prototype]]。
10.1.2 [[SetPrototypeOf]] ( V )
[[SetPrototypeOf]] 内部方法用于一个
- 返回
OrdinarySetPrototypeOf (O, V)。
10.1.2.1 OrdinarySetPrototypeOf ( O, V )
抽象操作 OrdinarySetPrototypeOf 接受两个参数：O（一个对象）和 V（一个对象或
- 将 current 设为 O.[[Prototype]]。
- 如果
SameValue (V, current) 为true ，则返回true 。 - 将 extensible 设为 O.[[Extensible]]。
- 如果 extensible 为
false ，则返回false 。 - 将 p 设为 V。
- 将 done 设为
false 。 - 重复以下步骤，直到 done 为
true ： - 将 O.[[Prototype]] 设为 V。
- 返回
true 。
10.1.3 [[IsExtensible]] ( )
[[IsExtensible]] 内部方法用于一个
- 返回
OrdinaryIsExtensible (O)。
10.1.3.1 OrdinaryIsExtensible ( O )
抽象操作 OrdinaryIsExtensible 接受一个参数 O（一个对象），并返回一个布尔值。调用时执行以下步骤：
- 返回 O.[[Extensible]]。
10.1.4 [[PreventExtensions]] ( )
[[PreventExtensions]] 内部方法用于一个
- 返回
OrdinaryPreventExtensions (O)。
10.1.4.1 OrdinaryPreventExtensions ( O )
抽象操作 OrdinaryPreventExtensions 接受一个参数 O（一个对象），并返回
- 将 O.[[Extensible]] 设置为
false 。 - 返回
true 。
10.1.5 [[GetOwnProperty]] ( P )
[[GetOwnProperty]] 内部方法用于一个
- 返回
OrdinaryGetOwnProperty (O, P)。
10.1.5.1 OrdinaryGetOwnProperty ( O, P )
抽象操作 OrdinaryGetOwnProperty 接受两个参数 O（一个对象）和 P（一个
10.1.6 [[DefineOwnProperty]] ( P, Desc )
普通对象的 [[DefineOwnProperty]] 内部方法接受两个参数：P（一个
- 返回 ?
OrdinaryDefineOwnProperty (O, P, Desc).
10.1.6.1 OrdinaryDefineOwnProperty（O, P, Desc）
抽象操作 OrdinaryDefineOwnProperty 接受参数 O（一个对象）、P（一个
- 令 current 为 ? O.[[GetOwnProperty]](P)。
- 令 extensible 为 ?
IsExtensible (O)。 - 返回
ValidateAndApplyPropertyDescriptor (O, P, extensible, Desc, current)。
10.1.6.2 IsCompatiblePropertyDescriptor（Extensible, Desc, Current）
抽象操作 IsCompatiblePropertyDescriptor 接受参数 Extensible（一个布尔值）、Desc（一个
- 返回
ValidateAndApplyPropertyDescriptor (undefined ,"" , Extensible, Desc, Current)。
10.1.6.3 ValidateAndApplyPropertyDescriptor（O, P, extensible, Desc, current）
抽象操作 ValidateAndApplyPropertyDescriptor 接受参数
O（一个对象或
断言 ：IsPropertyKey (P) 是true 。- 如果 current 是
undefined ，则- 如果 extensible 是
false ，返回false 。 - 如果 O 是
undefined ，返回true 。 - 如果
IsAccessorDescriptor (Desc) 是true ，则 - 否则，
- 返回
true 。
- 如果 extensible 是
断言 ：current 是一个完全填充的属性描述符 。- 如果 Desc 没有任何字段，返回
true 。 - 如果 current.[[Configurable]] 是
false ，则- 如果 Desc 有一个 [[Configurable]] 字段且 Desc.[[Configurable]] 是
true ，返回false 。 - 如果 Desc 有一个 [[Enumerable]] 字段且 Desc.[[Enumerable]]
不等于 current.[[Enumerable]]，返回
false 。 - 如果
IsGenericDescriptor (Desc) 是false 并且IsAccessorDescriptor (Desc) 不等于IsAccessorDescriptor (current)，返回false 。 - 如果
IsAccessorDescriptor (current) 是true，则 - 否则，如果 current.[[Writable]] 是
false ，则- 如果 Desc 有一个 [[Writable]] 字段且 Desc.[[Writable]] 是
true ，返回false 。 - 如果 Desc 有一个 [[Value]] 字段且
SameValue (Desc.[[Value]], current.[[Value]]) 是false ，返回false 。
- 如果 Desc 有一个 [[Writable]] 字段且 Desc.[[Writable]] 是
- 如果 Desc 有一个 [[Configurable]] 字段且 Desc.[[Configurable]] 是
- 如果 O 不是
undefined ，则- 如果
IsDataDescriptor (current) 是true 且IsAccessorDescriptor (Desc) 是true ，则- 如果 Desc 有一个 [[Configurable]] 字段，令 configurable 为 Desc.[[Configurable]]；否则令 configurable 为 current.[[Configurable]]。
- 如果 Desc 有一个 [[Enumerable]] 字段，令 enumerable 为 Desc.[[Enumerable]]；否则令 enumerable 为 current.[[Enumerable]]。
- 替换对象 O 中名为 P 的属性为一个
存取器属性 ，其 [[Configurable]] 和 [[Enumerable]] 属性分别设置为 configurable 和 enumerable，其 [[Get]] 和 [[Set]] 属性设置为 Desc 中相应字段的值，如果 Desc 有该字段，则设置为该字段的值，否则设置为属性的默认值 。
- 否则，如果
IsAccessorDescriptor (current) 是true 且IsDataDescriptor (Desc) 是true ，则- 如果 Desc 有一个 [[Configurable]] 字段，令 configurable 为 Desc.[[Configurable]]；否则令 configurable 为 current.[[Configurable]]。
- 如果 Desc 有一个 [[Enumerable]] 字段，令 enumerable 为 Desc.[[Enumerable]]；否则令 enumerable 为 current.[[Enumerable]]。
- 替换对象 O 中名为 P 的属性为一个
数据属性 ，其 [[Configurable]] 和 [[Enumerable]] 属性分别设置为 configurable 和 enumerable，其 [[Value]] 和 [[Writable]] 属性设置为 Desc 中相应字段的值，如果 Desc 有该字段，则设置为该字段的值，否则设置为属性的默认值 。
- 否则，
- 对于 Desc 的每个字段，将对象 O 中名为 P 的属性的相应属性设置为该字段的值。
- 如果
- 返回
true 。
10.1.7 [[HasProperty]]（P）
一个
- 返回 ?
OrdinaryHasProperty （O, P）。
10.1.7.1 OrdinaryHasProperty（O, P）
抽象操作 OrdinaryHasProperty 接受参数 O（一个对象）和 P（一个
- 令 hasOwn 为 ? O.[[GetOwnProperty]](P)。
- 如果 hasOwn 不是
undefined ，返回true 。 - 令 parent 为 ? O.[[GetPrototypeOf]]()。
- 如果 parent 不是
null ，则- 返回 ? parent.[[HasProperty]](P)。
- 返回
false 。
10.1.8 [[Get]] ( P, Receiver )
[[Get]] 内部方法用于一个
- 返回 ?
OrdinaryGet (O, P, Receiver).
10.1.8.1 OrdinaryGet ( O, P, Receiver )
抽象操作 OrdinaryGet 接受参数 O（一个对象）、P（一个
- 让 desc 等于 ? O.[[GetOwnProperty]](P)。
- 如果 desc 是
undefined ，则- 让 parent 等于 ? O.[[GetPrototypeOf]]()。
- 如果 parent 是
null ，返回undefined 。 - 返回 ? parent.[[Get]](P, Receiver)。
- 如果
IsDataDescriptor (desc) 是true ，返回 desc.[[Value]]。 断言 :IsAccessorDescriptor (desc) 是true 。- 让 getter 等于 desc.[[Get]]。
- 如果 getter 是
undefined ，返回undefined 。 - 返回 ?
Call (getter, Receiver)。
10.1.9 [[Set]] ( P, V, Receiver )
普通对象（
- 返回 ?
OrdinarySet (O, P, V, Receiver)。
10.1.9.1 OrdinarySet ( O, P, V, Receiver )
抽象操作 OrdinarySet 接受四个参数：O（对象），P（属性键），V（ECMAScript 语言值），和 Receiver（ECMAScript 语言值），并返回一个完成记录，可能是包含布尔值的正常完成记录，也可能是抛出异常的完成记录。调用时执行以下步骤：
- 让 ownDesc 为 ? O.[[GetOwnProperty]](P)。
- 返回 ?
OrdinarySetWithOwnDescriptor (O, P, V, Receiver, ownDesc)。
10.1.9.2 OrdinarySetWithOwnDescriptor ( O, P, V, Receiver, ownDesc )
抽象操作 OrdinarySetWithOwnDescriptor 接受五个参数：O（对象），P（属性键），V（ECMAScript
语言值），Receiver（ECMAScript 语言值），和 ownDesc（属性描述符或
- 如果 ownDesc 为
undefined ，则：- 让 parent 为 ? O.[[GetPrototypeOf]]()。
- 如果 parent 不为
null ，则：- 返回 ? parent.[[Set]](P, V, Receiver)。
- 否则：
- 将 ownDesc 设置为属性描述符 {[[Value]]:
undefined , [[Writable]]:true , [[Enumerable]]:true , [[Configurable]]:true }。
- 将 ownDesc 设置为属性描述符 {[[Value]]:
- 如果
IsDataDescriptor (ownDesc) 为true ，则：- 如果 ownDesc.[[Writable]] 为
false ，返回false 。 - 如果 Receiver
不是一个对象 ，返回false 。 - 让 existingDescriptor 为 ? Receiver.[[GetOwnProperty]](P)。
- 如果 existingDescriptor 不为
undefined ，则：- 如果
IsAccessorDescriptor (existingDescriptor) 为true ，返回false 。 - 如果 existingDescriptor.[[Writable]] 为
false ，返回false 。 - 让 valueDesc 为属性描述符 {[[Value]]: V}。
- 返回 ? Receiver.[[DefineOwnProperty]](P, valueDesc)。
- 如果
- 否则：
Assert : Receiver 当前没有属性 P。- 返回 ?
CreateDataProperty (Receiver, P, V)。
- 如果 ownDesc.[[Writable]] 为
Assert :IsAccessorDescriptor (ownDesc) 为true 。- 让 setter 为 ownDesc.[[Set]]。
- 如果 setter 为
undefined ，返回false 。 - 执行 ?
Call (setter, Receiver, «V»)。 - 返回
true 。
10.1.10 [[Delete]] ( P )
普通对象（
- 返回 ?
OrdinaryDelete (O, P)。
10.1.10.1 OrdinaryDelete ( O, P )
抽象操作 OrdinaryDelete 接受两个参数：O（对象）和 P（
- 让 desc 为 ? O.[[GetOwnProperty]](P)。
- 如果 desc 为
undefined ，返回true 。 - 如果 desc.[[Configurable]] 为
true ，则：- 从 O 中删除名称为 P 的自身属性。
- 返回
true 。
- 返回
false 。
10.1.11 [[OwnPropertyKeys]] ( )
普通对象（
- 返回
OrdinaryOwnPropertyKeys (O)。
10.1.11.1 OrdinaryOwnPropertyKeys ( O )
抽象操作 OrdinaryOwnPropertyKeys 接受一个参数 O（对象），并返回一个包含
10.1.12 OrdinaryObjectCreate ( proto [ , additionalInternalSlotsList ] )
抽象操作 OrdinaryObjectCreate 接受参数 proto（一个对象或
- 让 internalSlotsList 为 « [[Prototype]], [[Extensible]] »。
- 如果 additionalInternalSlotsList 存在，则将
internalSlotsList 设置为
列表连接 internalSlotsList 和 additionalInternalSlotsList 的结果。 - 让 O 为
MakeBasicObject (internalSlotsList)。 - 将 O.[[Prototype]] 设置为 proto。
- 返回 O。
尽管 OrdinaryObjectCreate 仅调用
10.1.13 OrdinaryCreateFromConstructor ( constructor, intrinsicDefaultProto [ , internalSlotsList ] )
抽象操作 OrdinaryCreateFromConstructor 接受参数 constructor（一个
断言 : intrinsicDefaultProto 是本规范定义的内建对象的名称。对应的对象必须是一个内建对象，旨在作为对象的 [[Prototype]] 值。- 让 proto 为 ?
GetPrototypeFromConstructor (constructor, intrinsicDefaultProto)。 - 如果 internalSlotsList 存在，令 slotsList 为 internalSlotsList。
- 否则，令 slotsList 为一个新的空
列表 。 - 返回
OrdinaryObjectCreate (proto, slotsList)。
10.1.14 GetPrototypeFromConstructor ( constructor, intrinsicDefaultProto )
抽象操作 GetPrototypeFromConstructor 接受参数 constructor（一个
断言 : intrinsicDefaultProto 是本规范定义的内建对象的名称。对应的对象必须是一个内建对象，旨在作为对象的 [[Prototype]] 值。- 令 proto 为 ?
Get (constructor,"prototype" )。 - 如果 proto
不是一个对象 ，则- 令 realm 为 ?
GetFunctionRealm (constructor)。 - 将 proto 设置为 realm 的名为 intrinsicDefaultProto 的内建对象。
- 令 realm 为 ?
- 返回 proto。
10.1.15 RequireInternalSlot ( O, internalSlot )
抽象操作 RequireInternalSlot 接受参数 O（一个
- 如果 O
不是一个对象 ，则抛出一个TypeError 异常。 - 如果 O 不具有一个 internalSlot 内部槽，则抛出一个
TypeError 异常。 - 返回
unused 。
10.2 ECMAScript 函数对象
ECMAScript
除了 [[Extensible]] 和 [[Prototype]] 外，ECMAScript
| 内部槽 | 类型 | 描述 |
|---|---|---|
| [[Environment]] |
一个 |
函数封闭的 |
| [[PrivateEnvironment]] |
一个 |
函数封闭的 |
| [[FormalParameters]] |
一个 |
定义函数正式参数列表的源文本的根解析节点。 |
| [[ECMAScriptCode]] |
一个 |
定义函数主体的源文本的根解析节点。 |
| [[ConstructorKind]] |
|
函数是否是派生类 |
| [[Realm]] |
一个 |
函数创建的 |
| [[ScriptOrModule]] |
一个 |
函数创建的脚本或模块。 |
| [[ThisMode]] |
|
定义 this 引用在函数的正式参数和代码体内如何被解释。this
指向词法上封闭函数的 |
| [[Strict]] | 一个布尔值 |
如果这是一个 |
| [[HomeObject]] | 一个对象 |
如果函数使用了 super，这是提供 [[GetPrototypeOf]] 的对象，从而开始
super 属性的查找。
|
| [[SourceText]] | 一系列 Unicode 码点 |
定义函数的 |
| [[Fields]] |
一个 |
如果函数是一个类，则这是一个列表，表示类的非静态字段及其对应的初始化器。 |
| [[PrivateMethods]] |
一个 |
如果函数是一个类，则这是一个列表，表示类的非静态私有方法和访问器。 |
| [[ClassFieldInitializerName]] |
一个字符串、一个符号、一个 |
如果函数作为类字段的初始化器创建，则用于 |
| [[IsClassConstructor]] | 一个布尔值 |
指示函数是否是一个类 |
所有 ECMAScript
10.2.1 [[Call]] ( thisArgument, argumentsList )
ECMAScript
- 让 callerContext 为
当前执行上下文 。 - 让 calleeContext 为
PrepareForOrdinaryCall (F,undefined )。 断言 : calleeContext 现在是当前执行上下文 。- 如果 F.[[IsClassConstructor]] 为
true ，则- 让 error 为一个新创建的
TypeError 对象。 - 注意：error 是在 calleeContext 中创建的，使用
F 关联的
领域记录 。 - 从
执行上下文栈 中移除 calleeContext，并将 callerContext 恢复为当前执行上下文 。 - 返回
ThrowCompletion (error)。
- 让 error 为一个新创建的
- 执行
OrdinaryCallBindThis (F, calleeContext, thisArgument)。 - 让 result 为
Completion (OrdinaryCallEvaluateBody (F, argumentsList))。 - 从
执行上下文栈 中移除 calleeContext，并将 callerContext 恢复为当前执行上下文 。 - 如果 result 是一个
返回完成 ，返回 result.[[Value]]。 ReturnIfAbrupt (result)。- 返回
undefined 。
10.2.1.1 PrepareForOrdinaryCall ( F, newTarget )
抽象操作 PrepareForOrdinaryCall 接受参数 F（一个 ECMAScript
- 让 callerContext 为
当前执行上下文 。 - 让 calleeContext 为一个新的
ECMAScript 代码执行上下文 。 - 将 calleeContext 的函数设置为 F。
- 让 calleeRealm 为 F.[[Realm]]。
- 将 calleeContext 的
领域 设置为 calleeRealm。 - 将 calleeContext 的 ScriptOrModule 设置为 F.[[ScriptOrModule]]。
- 让 localEnv 为
NewFunctionEnvironment (F, newTarget)。 - 将 calleeContext 的词法环境设置为 localEnv。
- 将 calleeContext 的变量环境设置为 localEnv。
- 将 calleeContext 的私有环境设置为 F.[[PrivateEnvironment]]。
- 如果 callerContext 尚未被挂起，则挂起 callerContext。
- 将 calleeContext 推入
执行上下文栈 ；calleeContext 现在是当前执行上下文 。 - 注意：此后产生的任何异常对象都与 calleeRealm 关联。
- 返回 calleeContext。
10.2.1.2 OrdinaryCallBindThis ( F, calleeContext, thisArgument )
抽象操作 OrdinaryCallBindThis 接受参数 F（一个 ECMAScript
- 让 thisMode 为 F.[[ThisMode]]。
- 如果 thisMode 是
lexical ，则返回unused 。 - 让 calleeRealm 为 F.[[Realm]]。
- 让 localEnv 为 calleeContext 的词法环境。
- 如果 thisMode 是
strict ，则：- 让 thisValue 为 thisArgument。
- 否则：
Assert : localEnv 是一个函数环境记录 。Assert : 下一步不会返回突发完成 ，因为 localEnv.[[ThisBindingStatus]] 不是initialized 。- 执行 ! localEnv.BindThisValue(thisValue)。
- 返回
unused 。
10.2.1.3 运行时语义：EvaluateBody
语法驱动操作
- 返回 ?
EvaluateFunctionBody 的FunctionBody ，参数为 functionObject 和 argumentsList。
- 返回 ?
EvaluateConciseBody 的ConciseBody ，参数为 functionObject 和 argumentsList。
- 返回 ?
EvaluateGeneratorBody 的GeneratorBody ，参数为 functionObject 和 argumentsList。
- 返回 ?
EvaluateAsyncGeneratorBody 的AsyncGeneratorBody ，参数为 functionObject 和 argumentsList。
- 返回 ?
EvaluateAsyncFunctionBody 的AsyncFunctionBody ，参数为 functionObject 和 argumentsList。
- 返回 ?
EvaluateAsyncConciseBody 的AsyncConciseBody ，参数为 functionObject 和 argumentsList。
断言 ：argumentsList 为空。断言 ：functionObject.[[ClassFieldInitializerName]] 不为空。- 如果
IsAnonymousFunctionDefinition (AssignmentExpression ) 为true ，则- 令 value 为 ?
NamedEvaluation 的Initializer ，参数为 functionObject.[[ClassFieldInitializerName]]。
- 令 value 为 ?
- 否则，
- 令 rhs 为 ?
Evaluation 的AssignmentExpression 。 - 令 value 为 ?
GetValue (rhs)。
- 令 rhs 为 ?
- 返回
完成记录 { [[Type]]:return , [[Value]]: value, [[Target]]:empty }。
尽管字段初始化器构成函数边界，调用
断言 ：argumentsList 为空。- 返回 ?
EvaluateClassStaticBlockBody 的ClassStaticBlockBody ，参数为 functionObject。
10.2.1.4 OrdinaryCallEvaluateBody ( F, argumentsList )
抽象操作 OrdinaryCallEvaluateBody 接受两个参数：F（一个 ECMAScript
- 返回 ?
EvaluateBody 的 F.[[ECMAScriptCode]]，参数为 F 和 argumentsList。
10.2.2 [[Construct]] ( argumentsList, newTarget )
ECMAScript
- 令 callerContext 为当前
运行执行上下文 。 - 令 kind 为 F.[[ConstructorKind]]。
- 如果 kind 为
base ，则- 令 thisArgument 为 ?
OrdinaryCreateFromConstructor (newTarget,"%Object.prototype%" )。
- 令 thisArgument 为 ?
- 令 calleeContext 为
PrepareForOrdinaryCall (F, newTarget)。 Assert : calleeContext 现在是运行执行上下文 。- 如果 kind 为
base ，则- 执行
OrdinaryCallBindThis (F, calleeContext, thisArgument)。 - 令 initializeResult 为
Completion (InitializeInstanceElements (thisArgument, F))。 - 如果 initializeResult 是
突发完成记录 ，则
- 执行
- 令 constructorEnv 为 calleeContext 的 LexicalEnvironment。
- 令 result 为
Completion (OrdinaryCallEvaluateBody (F, argumentsList))。 - 从
执行上下文栈 中移除 calleeContext，并将 callerContext 恢复为运行执行上下文 。 - 如果 result 是
返回完成记录 ，则- 如果 result.[[Value]]
是一个对象 ，返回 result.[[Value]]。 - 如果 kind 为
base ，返回 thisArgument。 - 如果 result.[[Value]] 不是
undefined ，则抛出一个TypeError 异常。
- 如果 result.[[Value]]
- 否则,
ReturnIfAbrupt (result)。
- 令 thisBinding 为 ? constructorEnv.GetThisBinding()。
Assert : thisBinding是一个对象 。- 返回 thisBinding。
10.2.3 OrdinaryFunctionCreate ( functionPrototype, sourceText, ParameterList, Body, thisMode, env, privateEnv )
抽象操作 OrdinaryFunctionCreate 接受以下参数：functionPrototype（一个对象），
sourceText（一系列 Unicode 代码点），ParameterList（一个
- 令 internalSlotsList 为
表 30 中列出的内部槽。 - 令 F 为
OrdinaryObjectCreate (functionPrototype, internalSlotsList)。 - 将 F.[[Call]] 设置为
10.2.1 中指定的定义。 - 将 F.[[SourceText]] 设置为 sourceText。
- 将 F.[[FormalParameters]] 设置为 ParameterList。
- 将 F.[[ECMAScriptCode]] 设置为 Body。
- 如果
source text matched by Body 是严格模式代码 ，则令 Strict 为true ；否则令 Strict 为false 。 - 将 F.[[Strict]] 设置为 Strict。
- 如果 thisMode 是
lexical-this ，则将 F.[[ThisMode]] 设置为lexical 。 - 否则如果 Strict 为
true ，则将 F.[[ThisMode]] 设置为strict 。 - 否则，将 F.[[ThisMode]] 设置为
global 。 - 将 F.[[IsClassConstructor]] 设置为
false 。 - 将 F.[[Environment]] 设置为 env。
- 将 F.[[PrivateEnvironment]] 设置为 privateEnv。
- 将 F.[[ScriptOrModule]] 设置为
GetActiveScriptOrModule ()。 - 将 F.[[Realm]] 设置为
当前 Realm 记录 。 - 将 F.[[HomeObject]] 设置为
undefined 。 - 将 F.[[Fields]] 设置为一个新的空的
列表 。 - 将 F.[[PrivateMethods]]
设置为一个新的空的
列表 。 - 将 F.[[ClassFieldInitializerName]] 设置为
empty 。 - 令 len 为
ParameterList 的期望参数数量。 - 执行
SetFunctionLength (F, len)。 - 返回 F。
10.2.4 AddRestrictedFunctionProperties ( F, realm )
抽象操作 AddRestrictedFunctionProperties 接受两个参数：F（一个
断言 : realm.[[Intrinsics]].[[%ThrowTypeError% ]] 存在 并已初始化。- 令 thrower 为 realm.[[Intrinsics]].[[
%ThrowTypeError% ]]。 - 执行 !
DefinePropertyOrThrow (F,"caller" , 属性描述符 { [[Get]]: thrower, [[Set]]: thrower, [[Enumerable]]:false , [[Configurable]]:true }). - 执行 !
DefinePropertyOrThrow (F,"arguments" , 属性描述符 { [[Get]]: thrower, [[Set]]: thrower, [[Enumerable]]:false , [[Configurable]]:true }). - 返回
unused 。
10.2.4.1 %ThrowTypeError% ( )
这个函数是 %ThrowTypeError% 内在对象。
它是一个匿名的内置
当调用时，它执行以下步骤：
- 抛出一个
TypeError 异常。
这个函数的 [[Extensible]] 内部槽的值为
这个函数的
这个函数的
10.2.5 MakeConstructor ( F [ , writablePrototype [ , prototype ] ] )
抽象操作 MakeConstructor 接受一个参数 F（一个 ECMAScript
- 如果 F 是一个 ECMAScript
函数对象 ， 则断言 :IsConstructor (F) 为false 。断言 : F 是一个可扩展的对象，且没有一个名为"prototype" 的自身属性。- 将 F.[[Construct]] 设置为
在
10.2.2 中指定的定义。
- 否则，
- 将 F.[[Construct]] 设置为
在
10.3.2 中指定的定义。
- 将 F.[[Construct]] 设置为
在
- 将 F.[[ConstructorKind]] 设置为
base 。 - 如果 writablePrototype 不存在，将 writablePrototype
设置为
true 。 - 如果 prototype 不存在，则
- 将 prototype 设置为
OrdinaryObjectCreate (%Object.prototype% )。 - 执行 !
DefinePropertyOrThrow (prototype,"constructor" , 属性描述符 { [[Value]]: F, [[Writable]]: writablePrototype, [[Enumerable]]:false , [[Configurable]]:true }).
- 将 prototype 设置为
- 执行 !
DefinePropertyOrThrow (F,"prototype" , 属性描述符 { [[Value]]: prototype, [[Writable]]: writablePrototype, [[Enumerable]]:false , [[Configurable]]:false }). - 返回
unused 。
10.2.6 MakeClassConstructor ( F )
抽象操作 MakeClassConstructor 接受一个参数 F（一个 ECMAScript
断言 : F.[[IsClassConstructor]] 为false 。- 将 F.[[IsClassConstructor]] 设置为
true 。 - 返回
unused 。
10.2.7 MakeMethod ( F, homeObject )
抽象操作 MakeMethod 接受参数 F（一个 ECMAScript
- 将 F.[[HomeObject]] 设置为 homeObject。
- 返回
unused 。
10.2.8 DefineMethodProperty ( homeObject, key, closure, enumerable )
抽象操作 DefineMethodProperty 接受四个参数：homeObject（一个对象），key（一个
断言 : homeObject 是一个普通的、可扩展的对象。- 如果 key 是一个
私有名称 ，则- 返回
PrivateElement { [[Key]]: key, [[Kind]]:method , [[Value]]: closure }。
- 返回
- 否则,
- 让 desc 为 PropertyDescriptor { [[Value]]: closure, [[Writable]]:
true , [[Enumerable]]: enumerable, [[Configurable]]:true }。 - 执行 ?
DefinePropertyOrThrow (homeObject, key, desc)。 - 注：
DefinePropertyOrThrow 仅在尝试定义一个类静态方法时，如果 key 为"prototype" ，才会返回突然完成 。 - 返回
unused 。
- 让 desc 为 PropertyDescriptor { [[Value]]: closure, [[Writable]]:
10.2.9 SetFunctionName ( F, name [ , prefix ] )
抽象操作 SetFunctionName 接受两个必需参数和一个可选参数：F（一个
断言 : F 是一个可扩展的对象，并且没有"name" 自有属性。- 如果 name
是一个符号 ，则- 让 description 为 name 的 [[Description]] 值。
- 如果 description 为
undefined ， 将 name 设置为空字符串。 - 否则，将 name 设置为
字符串连接 ， 包含"[" 、description 和"]" 。
- 否则，如果 name 是一个
私有名称 ，则- 将 name 设置为 name 的 [[Description]]。
- 如果 F 有一个 [[InitialName]]
内部槽，则
- 将 F.[[InitialName]] 设置为 name。
- 如果 prefix 存在，则
- 将 name 设置为
字符串连接 ， 包含 prefix、代码单元 0x0020（空格）和 name。 - 如果 F 有一个 [[InitialName]]
内部槽，则
- 可选地，将 F.[[InitialName]] 设置为 name。
- 将 name 设置为
- 执行 !
DefinePropertyOrThrow (F,"name" ，属性描述符 { [[Value]]: name, [[Writable]]:false ，[[Enumerable]]:false ，[[Configurable]]:true }). - 返回
unused 。
10.2.10 SetFunctionLength ( F, length )
抽象操作 SetFunctionLength 接受两个参数：F（一个
断言 : F 是一个可扩展的对象，并且没有"length" 自有属性。- 执行 !
DefinePropertyOrThrow (F,"length" ，属性描述符 { [[Value]]:𝔽 (length), [[Writable]]:false ，[[Enumerable]]:false ，[[Configurable]]:true }). - 返回
unused 。
10.2.11 FunctionDeclarationInstantiation ( func, argumentsList )
抽象操作 FunctionDeclarationInstantiation 接受两个参数：func（一个 ECMAScript
它在调用时执行以下步骤：
- 让 calleeContext 是
正在执行的执行上下文 。 - 让 code 是 func.[[ECMAScriptCode]]。
- 让 strict 是 func.[[Strict]]。
- 让 formals 是 func.[[FormalParameters]]。
- 让 parameterNames 是
绑定名称 的 formals。 - 如果 parameterNames 有任何重复项，令
hasDuplicates 为
true 。否则，令 hasDuplicates 为false 。 - 让 simpleParameterList 是
简单参数列表 的 formals。 - 让 hasParameterExpressions 是
包含表达式 的 formals。 - 让 varNames 是
变量声明名称 的 code。 - 让 varDeclarations 是
变量作用域声明 的 code。 - 让 lexicalNames 是
词法声明名称 的 code。 - 让 functionNames 是一个新的空的
列表 。 - 让 functionsToInitialize 是一个新的空的
列表 。 - 对于 varDeclarations 的每一个元素 d，
按照反向
列表 顺序，执行以下操作- 如果 d 既不是
变量声明 也不是ForBinding 也不是BindingIdentifier ，则
- 如果 d 既不是
- 让 argumentsObjectNeeded 为
true 。 - 如果 func.[[ThisMode]] 是
lexical ，则- 注: 箭头函数永远没有 arguments 对象。
- 将 argumentsObjectNeeded 设置为
false 。
- 否则，如果 parameterNames 包含
"arguments" ，则- 将 argumentsObjectNeeded 设置为
false 。
- 将 argumentsObjectNeeded 设置为
- 否则，如果 hasParameterExpressions 为
false ，则- 如果 functionNames 包含
"arguments" 或 lexicalNames 包含"arguments" ，则- 将 argumentsObjectNeeded 设置为
false 。
- 将 argumentsObjectNeeded 设置为
- 如果 functionNames 包含
- 如果 strict 为
true 或 hasParameterExpressions 为false ，则 - 否则,
- 注: 需要一个单独的
环境记录 以确保由直接 eval 调用在形式参数列表中创建的绑定在参数声明的环境之外。 - 让 calleeEnv 为 calleeContext 的 词法环境。
- 让 env 为
NewDeclarativeEnvironment (calleeEnv)。 断言 : calleeContext 的变量环境是 calleeEnv。- 将 calleeContext 的词法环境设置为 env。
- 注: 需要一个单独的
- 对于 parameterNames 中的每个字符串 paramName，执行
- 如果 argumentsObjectNeeded 为
true ，则- 如果 strict 为
true 或 simpleParameterList 为false ，则- 让 ao 为
CreateUnmappedArgumentsObject (argumentsList)。
- 让 ao 为
- 否则，
- 注: 映射的参数对象仅在
非严格模式函数 中提供，并且这些函数没有剩余参数、参数默认值初始化器或任何解构参数。 - 让 ao 为
CreateMappedArgumentsObject (func, formals, argumentsList, env)。
- 注: 映射的参数对象仅在
- 如果 strict 为
true ，则 - 否则，
- 执行
! env.CreateMutableBinding(
"arguments" ,false )。
- 执行
! env.CreateMutableBinding(
- 执行
! env.InitializeBinding(
"arguments" , ao)。 - 让 parameterBindings 为
list-concatenation 的 parameterNames 和 «"arguments" »。
- 如果 strict 为
- 否则，
- 让 parameterBindings 为 parameterNames。
- 让 iteratorRecord 为
CreateListIteratorRecord (argumentsList)。 - 如果 hasDuplicates 为
true ，则- 执行 ?
IteratorBindingInitialization 的 formals，使用参数 iteratorRecord 和undefined 。
- 执行 ?
- 否则，
- 执行 ?
IteratorBindingInitialization 的 formals，使用参数 iteratorRecord 和 env。
- 执行 ?
- 如果 hasParameterExpressions 为
false ，则 - 否则，
- 注: 需要一个单独的
环境记录 来确保在形式参数列表中创建的闭包无法访问函数体中的声明。 - 让 varEnv 为
NewDeclarativeEnvironment (env)。 - 将 calleeContext 的 VariableEnvironment 设置为 varEnv。
- 让 instantiatedVarNames 为一个新的空
列表 。 - 对于 varNames 中的每个元素 n，执行
- 如果 instantiatedVarNames 不包含 n，则
- 将 n 添加到 instantiatedVarNames。
- 执行
! varEnv.CreateMutableBinding(n,
false )。 - 如果 parameterBindings 不包含 n，或
functionNames 包含 n，则
- 让 initialValue 为
undefined 。
- 让 initialValue 为
- 否则，
- 让 initialValue 为
! env.GetBindingValue(n,
false )。
- 让 initialValue 为
! env.GetBindingValue(n,
- 执行 ! varEnv.InitializeBinding(n, initialValue)。
- 注: 与形式参数同名的变量最初具有与相应初始化参数相同的值。
- 如果 instantiatedVarNames 不包含 n，则
- 注: 需要一个单独的
- 注: 附录
B.3.2.1 在此处添加了额外的步骤。 - 如果 strict 为
false ，则 - 否则，
- 让 lexEnv 为 varEnv。
- 将 calleeContext 的 LexicalEnvironment 设置为 lexEnv。
- 让 lexDeclarations 为
词法作用域声明 的 code。 - 对于 lexDeclarations 中的每个元素 d，执行
- 让 privateEnv 为 calleeContext 的 PrivateEnvironment。
- 对于 functionsToInitialize 中的每个
解析节点 f，执行 - 返回
unused 。
10.3 内置函数对象
内置的
除了每个
内置
内置
内置
实现可以提供本规范中未定义的额外内置
10.3.1 [[Call]] ( thisArgument, argumentsList )
内置
- 返回 ?
BuiltinCallOrConstruct (F, thisArgument, argumentsList,undefined ).
10.3.2 [[Construct]] ( argumentsList, newTarget )
内置
- 返回 ?
BuiltinCallOrConstruct (F,uninitialized , argumentsList, newTarget).
10.3.3 BuiltinCallOrConstruct ( F, thisArgument, argumentsList, newTarget )
抽象操作 BuiltinCallOrConstruct 接受以下参数：F（一个内置的
- 让 callerContext 为当前
运行中的执行上下文 。 - 如果 callerContext 尚未被挂起，则挂起 callerContext。
- 让 calleeContext 为一个新的
执行上下文 。 - 将 calleeContext 的函数设置为 F。
- 让 calleeRealm 为 F.[[Realm]]。
- 将 calleeContext 的
Realm 设置为 calleeRealm。 - 将 calleeContext 的 ScriptOrModule 设置为
null 。 - 执行对 calleeContext 的任何必要的
实现定义 初始化。 - 将 calleeContext 推入
执行上下文栈 ；calleeContext 现在是运行中的执行上下文 。 - 让 result 为
完成记录 ，即以符合 F 规范的方式评估 F 的结果。如果 thisArgument 为uninitialized ，则this 的值为未初始化；否则，thisArgument 提供this 值。argumentsList 提供命名参数。newTarget 提供 NewTarget 值。 - 注：如果 F 在本文件中定义，“F 的规范”是通过算法步骤或其他方式指定的行为。
- 从
执行上下文栈 中移除 calleeContext，并将 callerContext 恢复为运行中的执行上下文 。 - 返回 ? result。
当 calleeContext 从
10.3.4 CreateBuiltinFunction ( behaviour, length, name, additionalInternalSlotsList [ , realm [ , prototype [ , prefix ] ] ] )
抽象操作 CreateBuiltinFunction 接受以下参数：behaviour（一个
- 如果 realm 不存在，则将 realm 设置为
当前 Realm 记录 。 - 如果 prototype 不存在，则将 prototype 设置为
realm.[[Intrinsics]].[[
%Function.prototype% ]]。 - 让 internalSlotsList 为一个
列表 ，包含所有10.3 对于即将创建的内置函数对象 所需的内部槽的名称。 - 将 additionalInternalSlotsList 的元素附加到 internalSlotsList。
- 让 func 为一个新的内置
函数对象 ，当调用时，它会根据 behaviour 的描述，使用提供的参数作为 behaviour 指定的相应参数的值。新的函数对象 具有名称为 internalSlotsList 元素的内部槽，并具有一个 [[InitialName]] 内部槽。 - 将 func.[[Prototype]] 设置为 prototype。
- 将 func.[[Extensible]] 设置为
true 。 - 将 func.[[Realm]] 设置为 realm。
- 将 func.[[InitialName]] 设置为
null 。 - 执行
SetFunctionLength (func, length)。 - 如果 prefix 不存在，则
- 执行
SetFunctionName (func, name)。
- 执行
- 否则，
- 执行
SetFunctionName (func, name, prefix)。
- 执行
- 返回 func。
本规范中定义的每个内置函数都是通过调用 CreateBuiltinFunction 抽象操作创建的。
10.4 内置的奇异对象内部方法和槽
本规范定义了几种内置的
10.4.1 绑定函数奇异对象
一个对象是一个 绑定函数奇异对象，如果它的 [[Call]] 和（如果适用的话）[[Construct]] 内部方法使用以下实现，并且它的其他基本内部方法使用在
| 内部槽 | 类型 | 描述 |
|---|---|---|
| [[BoundTargetFunction]] | 可调用的对象 |
封装的 |
| [[BoundThis]] |
一个 |
在调用封装的函数时始终传递的 |
| [[BoundArguments]] |
一个 |
一个值的列表，其元素作为对封装函数的任何调用的第一个参数。 |
10.4.1.1 [[Call]] ( thisArgument, argumentsList )
[[Call]] 内部方法用于一个
10.4.1.2 [[Construct]] ( argumentsList, newTarget )
[[Construct]] 内部方法用于一个
- 令 target 为 F.[[BoundTargetFunction]]。
断言 :IsConstructor (target) 为true 。- 令 boundArgs 为 F.[[BoundArguments]]。
- 令 args 为
列表连接 的 boundArgs 和 argumentsList。 - 如果
SameValue (F, newTarget) 为true ，则将 newTarget 设置为 target。 - 返回 ?
Construct (target, args, newTarget)。
10.4.1.3 BoundFunctionCreate ( targetFunction, boundThis, boundArgs )
抽象操作 BoundFunctionCreate 接受参数 targetFunction（一个
- 令 proto 为 ? targetFunction.[[GetPrototypeOf]]()。
- 令 internalSlotsList 为 «[[Prototype]]，[[Extensible]]» 和在
表 31 中列出的内部槽的列表连接 。 - 令 obj 为
MakeBasicObject (internalSlotsList)。 - 将 obj.[[Prototype]] 设置为 proto。
- 将 obj.[[Call]] 设置为在
10.4.1.1 中描述的内容。 - 如果
IsConstructor (targetFunction) 为true ，则：- 将 obj.[[Construct]] 设置为在
10.4.1.2 中描述的内容。
- 将 obj.[[Construct]] 设置为在
- 将 obj.[[BoundTargetFunction]] 设置为 targetFunction。
- 将 obj.[[BoundThis]] 设置为 boundThis。
- 将 obj.[[BoundArguments]] 设置为 boundArgs。
- 返回 obj。
10.4.2 数组奇异对象
数组是一个
一个对象是一个 数组奇异对象（或简称为数组），如果它的 [[DefineOwnProperty]]
内部方法使用以下实现，并且它的其他基本内部方法使用在
10.4.2.1 [[DefineOwnProperty]] ( P, Desc )
[[DefineOwnProperty]] 内部方法在
- 如果 P 是
"length" ，则- 返回 ?
ArraySetLength (A, Desc).
- 返回 ?
- 否则，如果 P 是一个
数组索引 ，则- 让 lengthDesc 为
OrdinaryGetOwnProperty (A,"length" ). Assert :IsDataDescriptor (lengthDesc) 是true 。Assert : lengthDesc.[[Configurable]] 是false 。- 让 length 为 lengthDesc.[[Value]]。
Assert : length 是一个非负的整数 。- 让 index 为 !
ToUint32 (P)。 - 如果 index ≥ length 且
lengthDesc.[[Writable]] 是
false ，则返回false 。 - 让 succeeded 为 !
OrdinaryDefineOwnProperty (A, P, Desc)。 - 如果 succeeded 是
false ，则返回false 。 - 如果 index ≥ length，则
- 将 lengthDesc.[[Value]] 设置为 index +
1 𝔽。 - 将 succeeded 设置为 !
OrdinaryDefineOwnProperty (A,"length" , lengthDesc)。 Assert : succeeded 是true 。
- 将 lengthDesc.[[Value]] 设置为 index +
- 返回
true 。
- 让 lengthDesc 为
- 返回 ?
OrdinaryDefineOwnProperty (A, P, Desc)。
10.4.2.2 ArrayCreate ( length [ , proto ] )
抽象操作 ArrayCreate 接受参数 length（一个非负的
- 如果 length > 232 - 1，抛出一个
RangeError 异常。 - 如果 proto 不存在，将 proto 设置为
%Array.prototype% 。 - 让 A 为
MakeBasicObject (« [[Prototype]], [[Extensible]] »)。 - 将 A.[[Prototype]] 设置为 proto。
- 将 A.[[DefineOwnProperty]]
设置为在
10.4.2.1 中规定的方式。 - 执行 !
OrdinaryDefineOwnProperty (A,"length" , 属性描述符 { [[Value]]:𝔽 (length), [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }）。 - 返回 A。
10.4.2.3 ArraySpeciesCreate ( originalArray, length )
抽象操作 ArraySpeciesCreate 接受两个参数：originalArray（一个对象）和 length（一个非负的
- 让 isArray 为 ?
IsArray (originalArray)。 - 如果 isArray 为
false ，返回 ?ArrayCreate (length)。 - 让 C 为 ?
Get (originalArray,"constructor" )。 - 如果
IsConstructor (C) 为true ，则- 让 thisRealm 为
当前 Realm 记录 。 - 让 realmC 为 ?
GetFunctionRealm (C)。 - 如果 thisRealm 和 realmC 不是同一个
Realm 记录 ，则
- 让 thisRealm 为
- 如果 C
是一个对象 ，则 - 如果 C 为
undefined ，返回 ?ArrayCreate (length)。 - 如果
IsConstructor (C) 为false ，抛出一个TypeError 异常。 - 返回 ?
Construct (C, «𝔽 (length) »)。
10.4.2.4 ArraySetLength ( A, Desc )
抽象操作 ArraySetLength 接受两个参数：A（一个数组）和 Desc（一个
- 如果 Desc 没有 [[Value]] 字段，则
- 返回 !
OrdinaryDefineOwnProperty (A,"length" , Desc).
- 返回 !
- 让 newLenDesc 为 Desc 的一个副本。
- 让 newLen 为
?
ToUint32 (Desc.[[Value]])。 - 让 numberLen 为
?
ToNumber (Desc.[[Value]])。 - 如果
SameValueZero (newLen, numberLen) 为false ，则抛出一个RangeError 异常。 - 将 newLenDesc.[[Value]] 设置为 newLen。
- 让 oldLenDesc 为 ?
OrdinaryGetOwnProperty (A,"length" )。 Assert ：IsDataDescriptor (oldLenDesc) 为true 。Assert ：oldLenDesc.[[Configurable]] 为false 。- 让 oldLen 为 oldLenDesc.[[Value]]。
- 如果 newLen ≥ oldLen，则
- 返回 !
OrdinaryDefineOwnProperty (A,"length" , newLenDesc).
- 返回 !
- 如果 oldLenDesc.[[Writable]] 为
false ，返回false 。 - 如果 newLenDesc 没有 [[Writable]] 字段，或者 newLenDesc.[[Writable]] 为
true ，则- 让 newWritable 为
true 。
- 让 newWritable 为
- 否则,
- 注意：将 [[Writable]] 属性设置为
false 是延迟的，以防某些元素无法被删除。 - 让 newWritable 为
false 。 - 将 newLenDesc.[[Writable]]
设置为
true 。
- 注意：将 [[Writable]] 属性设置为
- 让 succeeded 为 !
OrdinaryDefineOwnProperty (A,"length" , newLenDesc)。 - 如果 succeeded 为
false ，则返回false 。 - 对于 A 中每个拥有的
属性键 P，其中 P 是一个数组索引 ，并且 !ToUint32 (P) ≥ newLen，按降序数字索引顺序，执行- 让 deleteSucceeded 为 ! A.[[Delete]](P)。
- 如果 deleteSucceeded 为
false ，则- 将 newLenDesc.[[Value]] 设置为 !
ToUint32 (P) +1 𝔽。 - 如果 newWritable 为
false ，则将 newLenDesc.[[Writable]] 设置为false 。 - 执行 !
OrdinaryDefineOwnProperty (A,"length" , newLenDesc)。 - 返回
false 。
- 将 newLenDesc.[[Value]] 设置为 !
- 如果 newWritable 为
false ，则- 将 succeeded 设置为 !
OrdinaryDefineOwnProperty (A,"length" , 属性描述符 { [[Writable]]：false } )。 Assert ：succeeded 为true 。
- 将 succeeded 设置为 !
- 返回
true 。
10.4.3 字符串奇异对象
字符串对象是一个封装了字符串值的
如果一个对象的 [[GetOwnProperty]]、[[DefineOwnProperty]] 和 [[OwnPropertyKeys]] 内部方法使用以下实现，并且它的其他基本内部方法使用在
10.4.3.1 [[GetOwnProperty]] ( P )
一个
- 让 desc 为
OrdinaryGetOwnProperty (S, P). - 如果 desc 不为
undefined ，则返回 desc。 - 返回
StringGetOwnProperty (S, P).
10.4.3.2 [[DefineOwnProperty]] ( P, Desc )
一个
- 让 stringDesc 为
StringGetOwnProperty (S, P). - 如果 stringDesc 不为
undefined ，则：- 让 extensible 为 S.[[Extensible]]。
- 返回
IsCompatiblePropertyDescriptor (extensible, Desc, stringDesc).
- 返回 !
OrdinaryDefineOwnProperty (S, P, Desc).
10.4.3.3 [[OwnPropertyKeys]] ( )
一个
- 让 keys 为一个新的空
列表 。 - 让 str 为 O.[[StringData]]。
断言 : str是一个字符串 。- 让 len 为 str 的长度。
- 对每一个整数 i，使得 0 ≤ i < len，按升序执行：
- 对 O 的每一个自有属性键 P，使得 P 是一个
数组索引 并且 !ToIntegerOrInfinity (P) ≥ len，按升序的数字索引顺序执行：- 将 P 追加到 keys。
- 对 O 的每一个自有属性键 P，使得 P 是一个
字符串 并且 P 不是一个数组索引 ，按属性创建的时间顺序执行：- 将 P 追加到 keys。
- 对 O 的每一个自有属性键 P，使得 P 是一个
符号 ，按属性创建的时间顺序执行：- 将 P 追加到 keys。
- 返回 keys。
10.4.3.4 StringCreate ( value, prototype )
抽象操作 StringCreate 接受两个参数：value（一个字符串）和 prototype（一个对象），并返回一个
- 让 S 为
MakeBasicObject (« [[Prototype]], [[Extensible]], [[StringData]] »)。 - 将 S.[[Prototype]] 设置为 prototype。
- 将 S.[[StringData]] 设置为 value。
- 将 S.[[GetOwnProperty]] 设置为
10.4.3.1 中指定的内容。 - 将 S.[[DefineOwnProperty]] 设置为
10.4.3.2 中指定的内容。 - 将 S.[[OwnPropertyKeys]] 设置为
10.4.3.3 中指定的内容。 - 让 length 为 value 的长度。
- 执行 !
DefinePropertyOrThrow (S,"length" , 属性描述符 { [[Value]]:𝔽 (length), [[Writable]]:false , [[Enumerable]]:false , [[Configurable]]:false })。 - 返回 S。
10.4.3.5 StringGetOwnProperty ( S, P )
抽象操作 StringGetOwnProperty 接受两个参数：S（一个具有 [[StringData]] 内部槽的对象）和
P（一个
- 如果 P
不是一个字符串 ，返回undefined 。 - 让 index 为
CanonicalNumericIndexString (P)。 - 如果 index 是
undefined ，返回undefined 。 - 如果
IsIntegralNumber (index) 是false ，返回undefined 。 - 如果 index 是
-0 𝔽，返回undefined 。 - 让 str 为 S.[[StringData]]。
Assert : str是一个字符串 。- 让 len 为 str 的长度。
- 如果
ℝ (index) < 0 或 len ≤ℝ (index)，返回undefined 。 - 让 resultStr 为
str 从ℝ (index) 到ℝ (index) + 1 的子字符串。 - 返回属性描述符 { [[Value]]:
resultStr, [[Writable]]:
false , [[Enumerable]]:true , [[Configurable]]:false }。
10.4.4 Arguments Exotic Objects
大多数 ECMAScript 函数会向其代码提供一个 arguments 对象。根据函数定义的特性，其 arguments 对象可能是一个
如果一个对象的内部方法使用以下实现（未在此处指定的使用
虽然
Object.prototype.toString (
ParameterMap 对象及其属性值用作指定 arguments 对象与参数绑定之间对应关系的设备。ParameterMap 对象及其属性值并不直接从 ECMAScript 代码中可观察。ECMAScript 实现不需要实际创建或使用此类对象来实现指定的语义。
普通 arguments 对象定义了一个不可配置的
ECMAScript 对
10.4.4.1 [[GetOwnProperty]] ( P )
[[GetOwnProperty]] 内部方法用于
- 令 desc 为
OrdinaryGetOwnProperty (args, P)。 - 如果 desc 为
undefined ，则返回undefined 。 - 令 map 为 args.[[ParameterMap]]。
- 令 isMapped 为 !
HasOwnProperty (map, P)。 - 如果 isMapped 为
true ，则- 将 desc.[[Value]] 设置为
!
Get (map, P)。
- 将 desc.[[Value]] 设置为
!
- 返回 desc。
10.4.4.2 [[DefineOwnProperty]] ( P, Desc )
[[DefineOwnProperty]] 内部方法用于
- 令 map 为 args.[[ParameterMap]]。
- 令 isMapped 为 !
HasOwnProperty (map, P)。 - 令 newArgDesc 为 Desc。
- 如果 isMapped 为
true 且IsDataDescriptor (Desc) 为true ，则- 如果 Desc 没有 [[Value]]
字段，Desc 有一个
[[Writable]] 字段，且 Desc.[[Writable]] 为
false ，则- 将 newArgDesc 设置为 Desc 的副本。
- 将 newArgDesc.[[Value]] 设置为
!
Get (map, P)。
- 如果 Desc 没有 [[Value]]
字段，Desc 有一个
[[Writable]] 字段，且 Desc.[[Writable]] 为
- 令 allowed 为 !
OrdinaryDefineOwnProperty (args, P, newArgDesc)。 - 如果 allowed 为
false ，则返回false 。 - 如果 isMapped 为
true ，则- 如果
IsAccessorDescriptor (Desc) 为true ，则- 执行 ! map.[[Delete]](P)。
- 否则，
- 如果
- 返回
true 。
10.4.4.3 [[Get]] ( P, Receiver )
[[Get]] 内部方法用于
- 令 map 为 args.[[ParameterMap]]。
- 令 isMapped 为 !
HasOwnProperty (map, P)。 - 如果 isMapped 为
false ，则- 返回 ?
OrdinaryGet (args, P, Receiver)。
- 返回 ?
- 否则，
10.4.4.4 [[Set]] ( P, V, Receiver )
[[Set]] 内部方法用于
- 如果
SameValue (args, Receiver) 为false ，则- 令 isMapped 为
false 。
- 令 isMapped 为
- 否则，
- 令 map 为 args.[[ParameterMap]]。
- 令 isMapped 为 !
HasOwnProperty (map, P)。
- 如果 isMapped 为
true ，则 - 返回 ?
OrdinarySet (args, P, V, Receiver)。
10.4.4.5 [[Delete]] ( P )
[[Delete]] 内部方法用于
- 令 map 为 args.[[ParameterMap]]。
- 令 isMapped 为 !
HasOwnProperty (map, P)。 - 令 result 为 ?
OrdinaryDelete (args, P)。 - 如果 result 为
true 且 isMapped 为true ，则- 执行 ! map.[[Delete]](P)。
- 返回 result。
10.4.4.6 CreateUnmappedArgumentsObject ( argumentsList )
抽象操作 CreateUnmappedArgumentsObject 接受一个参数 argumentsList（一个
- 令 len 为 argumentsList 中的元素数量。
- 令 obj 为
OrdinaryObjectCreate (%Object.prototype% , « [[ParameterMap]] »). - 将 obj.[[ParameterMap]] 设置为
undefined 。 - 执行 !
DefinePropertyOrThrow (obj,"length" , 属性描述符 { [[Value]]:𝔽 (len), [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true }). - 令 index 为 0。
- 重复，直到 index < len，
- 令 val 为 argumentsList[index]。
- 执行 !
CreateDataPropertyOrThrow (obj, !ToString (𝔽 (index)), val)。 - 将 index 设置为 index + 1。
- 执行 !
DefinePropertyOrThrow (obj,@@iterator , 属性描述符 { [[Value]]: %Array.prototype.values%, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true }). - 执行 !
DefinePropertyOrThrow (obj,"callee" , 属性描述符 { [[Get]]:%ThrowTypeError% , [[Set]]:%ThrowTypeError% , [[Enumerable]]:false , [[Configurable]]:false }). - 返回 obj。
10.4.4.7 CreateMappedArgumentsObject ( func, formals, argumentsList, env )
抽象操作 CreateMappedArgumentsObject 接受参数 func（一个对象）、formals（一个
断言 ：formals 不包含剩余参数、任何绑定模式或任何初始化器。它可以包含重复的标识符。- 令 len 为 argumentsList 中元素的数量。
- 令 obj 为
MakeBasicObject (« [[Prototype]], [[Extensible]], [[ParameterMap]] »)。 - 设置 obj.[[GetOwnProperty]] 如
10.4.4.1 所述。 - 设置 obj.[[DefineOwnProperty]]
如
10.4.4.2 所述。 - 设置 obj.[[Get]] 如
10.4.4.3 所述。 - 设置 obj.[[Set]] 如
10.4.4.4 所述。 - 设置 obj.[[Delete]] 如
10.4.4.5 所述。 - 设置 obj.[[Prototype]] 为
%Object.prototype% 。 - 令 map 为
OrdinaryObjectCreate (null )。 - 设置 obj.[[ParameterMap]] 为 map。
- 令 parameterNames 为
BoundNames 的 formals。 - 令 numberOfParameters 为 parameterNames 中元素的数量。
- 令 index 为 0。
- 重复，直到 index < len，
- 令 val 为 argumentsList[index]。
- 执行 !
CreateDataPropertyOrThrow (obj, !ToString (𝔽 (index)), val)。 - 设置 index 为 index + 1。
- 执行 !
DefinePropertyOrThrow (obj,"length" , PropertyDescriptor { [[Value]]:𝔽 (len), [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true })。 - 令 mappedNames 为一个新的空的
列表 。 - 设置 index 为 numberOfParameters - 1。
- 重复，直到 index ≥ 0，
- 令 name 为 parameterNames[index]。
- 如果 mappedNames 不包含 name，那么
- 将 name 添加到 mappedNames。
- 如果 index < len，那么
- 令 g 为
MakeArgGetter (name, env)。 - 令 p 为
MakeArgSetter (name, env)。 - 执行 ! map.[[DefineOwnProperty]](!
ToString (𝔽 (index)), PropertyDescriptor { [[Set]]: p, [[Get]]: g, [[Enumerable]]:false , [[Configurable]]:true })。
- 令 g 为
- 设置 index 为 index - 1。
- 执行 !
DefinePropertyOrThrow (obj,@@iterator , PropertyDescriptor { [[Value]]: %Array.prototype.values%, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true })。 - 执行 !
DefinePropertyOrThrow (obj,"callee" , PropertyDescriptor { [[Value]]: func, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true })。 - 返回 obj。
10.4.4.7.1 MakeArgGetter ( name, env )
抽象操作 MakeArgGetter 接受参数 name（一个字符串）和 env（一个
- 令 getterClosure 为一个新的
抽象闭包 ，无参数，捕获 name 和 env，并在调用时执行以下步骤：- 返回 env.GetBindingValue(name,
false )。
- 返回 env.GetBindingValue(name,
- 令 getter 为
CreateBuiltinFunction (getterClosure, 0,"" , « »)。 - 注意：getter 从不直接被 ECMAScript 代码访问。
- 返回 getter。
10.4.4.7.2 MakeArgSetter ( name, env )
抽象操作 MakeArgSetter 接受参数 name（一个字符串）和 env（一个
- 令 setterClosure 为一个新的
抽象闭包 ，参数为 (value)，捕获 name 和 env，并在调用时执行以下步骤：- 返回 ! env.SetMutableBinding(name,
value,
false )。
- 返回 ! env.SetMutableBinding(name,
value,
- 令 setter 为
CreateBuiltinFunction (setterClosure, 1,"" , « »)。 - 注意：setter 从不直接被 ECMAScript 代码访问。
- 返回 setter。
10.4.5 TypedArray 特殊对象
如果一个对象的 [[GetOwnProperty]]、[[HasProperty]]、[[DefineOwnProperty]]、[[Get]]、[[Set]]、[[Delete]] 和 [[OwnPropertyKeys]] 内部方法使用本节中的定义，并且其其他基本内部方法使用
10.4.5.1 [[GetOwnProperty]] ( P )
[[GetOwnProperty]] 是
-
如果 P
是一个字符串 ，则：-
令 numericIndex 为
CanonicalNumericIndexString (P)。 -
如果 numericIndex 不是
undefined ，则：-
令 value 为
TypedArrayGetElement (O, numericIndex)。 -
如果 value 是
undefined ，则返回undefined 。 -
返回属性描述符 { [[Value]]:
value, [[Writable]]:
true , [[Enumerable]]:true , [[Configurable]]:true }。
-
令 value 为
-
令 numericIndex 为
-
返回
OrdinaryGetOwnProperty (O, P)。
10.4.5.2 [[HasProperty]] ( P )
[[HasProperty]] 是
-
如果 P
是一个字符串 ，则：-
令 numericIndex 为
CanonicalNumericIndexString (P)。 -
如果 numericIndex 不是
undefined ，返回IsValidIntegerIndex (O, numericIndex)。
-
令 numericIndex 为
-
返回 ?
OrdinaryHasProperty (O, P)。
10.4.5.3 [[DefineOwnProperty]] ( P, Desc )
[[DefineOwnProperty]] 是
-
如果 P
是一个字符串 ，则：-
令 numericIndex 为
CanonicalNumericIndexString (P)。 -
如果 numericIndex 不是
undefined ，则：-
如果
IsValidIntegerIndex (O, numericIndex) 为false ，则返回false 。 -
如果 Desc 具有 [[Configurable]] 字段且 Desc.[[Configurable]] 为
false ，则返回false 。 -
如果 Desc 具有 [[Enumerable]] 字段且 Desc.[[Enumerable]] 为
false ，则返回false 。 -
如果
IsAccessorDescriptor (Desc) 为true ，则返回false 。 -
如果 Desc 具有 [[Writable]]
字段且 Desc.[[Writable]] 为
false ，则返回false 。 -
如果 Desc 具有 [[Value]]
字段，执行 ?
TypedArraySetElement (O, numericIndex, Desc.[[Value]])。 -
返回
true 。
-
如果
-
令 numericIndex 为
-
返回 !
OrdinaryDefineOwnProperty (O, P, Desc)。
10.4.5.4 [[Get]] ( P, Receiver )
[[Get]] 是
-
如果 P
是一个字符串 ，则：-
令 numericIndex 为
CanonicalNumericIndexString (P)。 -
如果 numericIndex 不是
undefined ，则：-
返回
TypedArrayGetElement (O, numericIndex)。
-
返回
-
令 numericIndex 为
-
返回 ?
OrdinaryGet (O, P, Receiver)。
10.4.5.5 [[Set]] ( P, V, Receiver )
[[Set]] 是
-
如果 P
是一个字符串 ，则：-
令 numericIndex 为
CanonicalNumericIndexString (P)。 -
如果 numericIndex 不是
undefined ，则：-
如果
SameValue (O, Receiver) 为true ，则：-
执行 ?
TypedArraySetElement (O, numericIndex, V)。 -
返回
true 。
-
执行 ?
-
如果
IsValidIntegerIndex (O, numericIndex) 为false ，则返回true 。
-
如果
-
令 numericIndex 为
-
返回 ?
OrdinarySet (O, P, V, Receiver)。
10.4.5.6 [[Delete]] ( P )
[[Delete]] 是
-
如果 P
是一个字符串 ，则：-
令 numericIndex 为
CanonicalNumericIndexString (P)。 -
如果 numericIndex 不是
undefined ，则：-
如果
IsValidIntegerIndex (O, numericIndex) 为false ，则返回true ；否则返回false 。
-
如果
-
令 numericIndex 为
-
返回 !
OrdinaryDelete (O, P)。
10.4.5.7 [[OwnPropertyKeys]] ( )
[[OwnPropertyKeys]] 是
-
令 taRecord 为
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst )。 -
令 keys 为一个新的空的
列表 。 -
如果
IsTypedArrayOutOfBounds (taRecord) 为false ，则：-
令 length 为
TypedArrayLength (taRecord)。 -
对于每个满足 0 ≤ i < length 的
整数 i，按升序进行：
-
令 length 为
-
对于每个 O 的自身
属性键 P，如果 P是一个字符串 并且 P 不是一个整数索引 ，按属性创建的时间顺序升序进行：- 将 P 添加到 keys。
-
对于每个 O 的自身
属性键 P，如果 P是一个符号 ，按属性创建的时间顺序升序进行：- 将 P 添加到 keys。
- 返回 keys。
10.4.5.8 带缓冲见证记录的 TypedArray
一个 带缓冲见证记录的 TypedArray 是一个
带缓冲见证记录的 TypedArray 具有
| 字段名称 | 值 | 含义 |
|---|---|---|
| [[Object]] | 一个 |
其缓冲区的字节长度被加载的 |
| [[CachedBufferByteLength]] | 一个非负的 |
创建 |
10.4.5.9 MakeTypedArrayWithBufferWitnessRecord ( obj, order )
抽象操作 MakeTypedArrayWithBufferWitnessRecord 接受参数 obj（一个
- 令 buffer 为 obj.[[ViewedArrayBuffer]]。
-
如果
IsDetachedBuffer (buffer) 为true ，则：-
令 byteLength 为
detached 。
-
令 byteLength 为
-
否则，
-
令 byteLength 为
ArrayBufferByteLength (buffer, order)。
-
令 byteLength 为
-
返回
带缓冲见证记录的 TypedArray { [[Object]]: obj, [[CachedBufferByteLength]]: byteLength }。
10.4.5.10 TypedArrayCreate ( prototype )
抽象操作 TypedArrayCreate 接受参数 prototype（一个对象），并返回一个
- 令 internalSlotsList 为 « [[Prototype]], [[Extensible]], [[ViewedArrayBuffer]], [[TypedArrayName]], [[ContentType]], [[ByteLength]], [[ByteOffset]], [[ArrayLength]] »。
-
令 A 为
MakeBasicObject (internalSlotsList)。 -
设置 A.[[GetOwnProperty]] 如
10.4.5.1 中所指定的。 -
设置 A.[[HasProperty]] 如
10.4.5.2 中所指定的。 -
设置 A.[[DefineOwnProperty]] 如
10.4.5.3 中所指定的。 -
设置 A.[[Get]] 如
10.4.5.4 中所指定的。 -
设置 A.[[Set]] 如
10.4.5.5 中所指定的。 -
设置 A.[[Delete]] 如
10.4.5.6 中所指定的。 -
设置 A.[[OwnPropertyKeys]] 如
10.4.5.7 中所指定的。 - 将 A.[[Prototype]] 设置为 prototype。
- 返回 A。
10.4.5.11 TypedArrayByteLength ( taRecord )
抽象操作 TypedArrayByteLength 接受参数 taRecord（一个
-
如果
IsTypedArrayOutOfBounds (taRecord) 为true ，则返回 0。 -
令 length 为
TypedArrayLength (taRecord)。 - 如果 length = 0，则返回 0。
- 令 O 为 taRecord.[[Object]]。
-
如果 O.[[ByteLength]] 不为
auto ，则返回 O.[[ByteLength]]。 -
令 elementSize 为
TypedArrayElementSize (O)。 - 返回 length × elementSize。
10.4.5.12 TypedArrayLength ( taRecord )
抽象操作 TypedArrayLength 接受参数 taRecord（一个
-
断言 ：IsTypedArrayOutOfBounds (taRecord) 为false 。 - 令 O 为 taRecord.[[Object]]。
-
如果 O.[[ArrayLength]] 不为
auto ，则返回 O.[[ArrayLength]]。 -
断言 ：IsFixedLengthArrayBuffer (O.[[ViewedArrayBuffer]]) 为false 。 - 令 byteOffset 为 O.[[ByteOffset]]。
-
令 elementSize 为
TypedArrayElementSize (O)。 - 令 byteLength 为 taRecord.[[CachedBufferByteLength]]。
-
断言 ：byteLength 不为detached 。 -
返回
floor ((byteLength - byteOffset) / elementSize)。
10.4.5.13 IsTypedArrayOutOfBounds ( taRecord )
抽象操作 IsTypedArrayOutOfBounds 接受参数 taRecord（一个
- 令 O 为 taRecord.[[Object]]。
- 令 bufferByteLength 为 taRecord.[[CachedBufferByteLength]]。
-
断言 ：如果 O.[[ViewedArrayBuffer]] 为IsDetachedBuffer ，则 bufferByteLength 必须为detached 。 -
如果 bufferByteLength 为
detached ，返回true 。 - 令 byteOffsetStart 为 O.[[ByteOffset]]。
-
如果 O.[[ArrayLength]] 为
auto ，则：- 令 byteOffsetEnd 为 bufferByteLength。
-
否则，
-
令 elementSize 为
TypedArrayElementSize (O)。 - 令 byteOffsetEnd 为 byteOffsetStart + O.[[ArrayLength]] × elementSize。
-
令 elementSize 为
-
如果 byteOffsetStart > bufferByteLength 或
byteOffsetEnd > bufferByteLength，返回
true 。 -
注意：长度为 0 的
TypedArrays 不被视为越界。 -
返回
false 。
10.4.5.14 IsValidIntegerIndex ( O, index )
抽象操作 IsValidIntegerIndex 接受参数 O（一个
-
如果
IsDetachedBuffer (O.[[ViewedArrayBuffer]]) 为true ，返回false 。 -
如果
IsIntegralNumber (index) 为false ，返回false 。 -
如果 index 是
-0 𝔽，返回false 。 -
令 taRecord 为
MakeTypedArrayWithBufferWitnessRecord (O,unordered )。 -
注意：当 O 的后备缓冲区是一个
可增长的 SharedArrayBuffer 时，边界检查不是同步操作。 -
如果
IsTypedArrayOutOfBounds (taRecord) 为true ，返回false 。 -
令 length 为
TypedArrayLength (taRecord)。 -
如果
ℝ (index) < 0 或ℝ (index) ≥ length，返回false 。 -
返回
true 。
10.4.5.15 TypedArrayGetElement ( O, index )
抽象操作 TypedArrayGetElement 接受参数 O（一个
-
如果
IsValidIntegerIndex (O, index) 为false ，返回undefined 。 - 令 offset 为 O.[[ByteOffset]]。
-
令 elementSize 为
TypedArrayElementSize (O)。 -
令 byteIndexInBuffer 为 (
ℝ (index) × elementSize) + offset。 -
令 elementType 为
TypedArrayElementType (O)。 -
返回
GetValueFromBuffer (O.[[ViewedArrayBuffer]], byteIndexInBuffer, elementType,true ,unordered )。
10.4.5.16 TypedArraySetElement ( O, index, value )
抽象操作 TypedArraySetElement 接受参数 O（一个
-
如果 O.[[ContentType]] 为
bigint ，令 numValue 为 ?ToBigInt (value)。 -
否则，令 numValue 为 ?
ToNumber (value)。 -
如果
IsValidIntegerIndex (O, index) 为true ，则：- 令 offset 为 O.[[ByteOffset]]。
-
令 elementSize 为
TypedArrayElementSize (O)。 -
令 byteIndexInBuffer 为 (
ℝ (index) × elementSize) + offset。 -
令 elementType 为
TypedArrayElementType (O)。 -
执行
SetValueInBuffer (O.[[ViewedArrayBuffer]], byteIndexInBuffer, elementType, numValue,true ,unordered )。
-
返回
unused 。
此操作似乎总是成功，但在尝试写入
10.4.5.17 IsArrayBufferViewOutOfBounds ( O )
抽象操作 IsArrayBufferViewOutOfBounds 接受参数 O（一个
-
如果 O 具有 [[DataView]] 内部插槽，则：
-
令 viewRecord 为
MakeDataViewWithBufferWitnessRecord (O,seq-cst )。 -
返回
IsViewOutOfBounds (viewRecord)。
-
令 viewRecord 为
-
令 taRecord 为
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst )。 -
返回
IsTypedArrayOutOfBounds (taRecord)。
10.4.6 模块命名空间特殊对象
一个 export * 语法间接导出的绑定。每个字符串值自身属性键是相应导出绑定名称的
一个对象是一个 模块命名空间特殊对象，如果它的 [[GetPrototypeOf]],
[[SetPrototypeOf]], [[IsExtensible]], [[PreventExtensions]], [[GetOwnProperty]], [[DefineOwnProperty]], [[HasProperty]], [[Get]], [[Set]], [[Delete]],
和
[[OwnPropertyKeys]] 内部方法使用本节中的定义，而它的其他基本内部方法使用
10.4.6.1 [[GetPrototypeOf]] ( )
一个
- 返回
null 。
10.4.6.2 [[SetPrototypeOf]] ( V )
一个
- 返回 !
SetImmutablePrototype (O, V)。
10.4.6.3 [[IsExtensible]] ( )
一个
- 返回
false 。
10.4.6.4 [[PreventExtensions]] ( )
一个
- 返回
true 。
10.4.6.5 [[GetOwnProperty]] ( P )
一个
- 如果 P
是一个符号 ，返回OrdinaryGetOwnProperty (O, P)。 - 让 exports 成为 O 的 [[Exports]]。
- 如果 exports 不包含 P，返回
undefined 。 - 让 value 成为 ? O.[[Get]](P, O)。
- 返回 PropertyDescriptor { [[Value]]:
value, [[Writable]]:
true , [[Enumerable]]:true , [[Configurable]]:false }。
10.4.6.6 [[DefineOwnProperty]] ( P, Desc )
一个
- 如果 P
是一个符号 ，返回 !OrdinaryDefineOwnProperty (O, P, Desc)。 - 让 current 成为 ? O.[[GetOwnProperty]](P)。
- 如果 current 是
undefined ，返回false 。 - 如果 Desc 具有 [[Configurable]]
字段，并且 Desc 的 [[Configurable]] 是
true ，返回false 。 - 如果 Desc 具有 [[Enumerable]]
字段，并且 Desc 的 [[Enumerable]] 是
false ，返回false 。 - 如果
IsAccessorDescriptor (Desc) 是true ，返回false 。 - 如果 Desc 具有 [[Writable]] 字段，并且
Desc 的 [[Writable]] 是
false ，返回false 。 - 如果 Desc 具有 [[Value]] 字段，返回
SameValue (Desc.[[Value]], current.[[Value]])。 - 返回
true 。
10.4.6.7 [[HasProperty]] ( P )
一个
- 如果 P
是一个符号 ，返回 !OrdinaryHasProperty (O, P)。 - 让 exports 成为 O 的 [[Exports]]。
- 如果 exports 包含 P，返回
true 。 - 返回
false 。
10.4.6.8 [[Get]] ( P, Receiver )
一个
- 如果 P
是一个符号 ，则- 返回 !
OrdinaryGet (O, P, Receiver)。
- 返回 !
- 让 exports 成为 O 的 [[Exports]]。
- 如果 exports 不包含 P，返回
undefined 。 - 让 m 成为 O 的 [[Module]]。
- 让 binding 成为 m.ResolveExport(P)。
断言 ：binding 是一个已解析绑定记录 。- 让 targetModule 成为 binding 的 [[Module]]。
断言 ：targetModule 不是undefined 。- 如果 binding 的 [[BindingName]]
是
namespace ，则- 返回
GetModuleNamespace (targetModule)。
- 返回
- 让 targetEnv 成为 targetModule 的 [[Environment]]。
- 如果 targetEnv 是
empty ，抛出一个ReferenceError 异常。 - 返回
? targetEnv.GetBindingValue(binding.[[BindingName]],
true )。
ResolveExport 是无副作用的。每次用特定的 exportName 和 resolveSet
参数调用此操作时，它必须返回相同的结果。实现可以选择预先计算或缓存每个
10.4.6.9 [[Set]] ( P, V, Receiver )
一个
- 返回
false 。
10.4.6.10 [[Delete]] ( P )
一个
- 如果 P
是一个符号 ，则- 返回 !
OrdinaryDelete (O, P)。
- 返回 !
- 让 exports 成为 O 的 [[Exports]]。
- 如果 exports 包含 P，返回
false 。 - 返回
true 。
10.4.6.11 [[OwnPropertyKeys]] ( )
一个
- 让 exports 成为 O 的 [[Exports]]。
- 让 symbolKeys 成为
OrdinaryOwnPropertyKeys (O)。 - 返回
列表连接 exports 和 symbolKeys。
10.4.6.12 ModuleNamespaceCreate ( module, exports )
抽象操作 ModuleNamespaceCreate 接收参数 module（一个
断言 ：module 的 [[Namespace]] 是empty 。- 让 internalSlotsList 成为
表 33 中列出的内部插槽。 - 让 M 成为
MakeBasicObject (internalSlotsList)。 - 将 M 的基本内部方法设置为
10.4.6 中的定义。 - 将 M 的 [[Module]] 设置为 module。
- 让 sortedExports 成为
列表 ，其元素是 exports 的元素，顺序就像用 %Array.prototype.sort% 使用undefined 作为 comparefn 对这些值进行排序一样。 - 将 M 的 [[Exports]] 设置为 sortedExports。
- 创建与
28.3 中定义相对应的 M 自身属性。 - 将 module 的 [[Namespace]] 设置为 M。
- 返回 M。
10.4.7 不可变原型特殊对象
一个
如果对象的 [[SetPrototypeOf]] 内部方法使用以下实现，则该对象是一个 不可变原型特殊对象。（其其他基本内部方法可以根据具体的
与其他
10.4.7.1 [[SetPrototypeOf]] ( V )
一个
- 返回 ?
SetImmutablePrototype (O, V)。
10.4.7.2 SetImmutablePrototype ( O, V )
抽象操作 SetImmutablePrototype 接收参数 O（一个对象）和 V（一个对象或
- 让 current 成为 ? O.[[GetPrototypeOf]]()。
- 如果
SameValue (V, current) 是true ，返回true 。 - 返回
false 。
10.5 代理对象的内部方法和内部插槽
代理对象是一个
如果对象的基本内部方法（包括 [[Call]] 和 [[Construct]]，如果适用）使用本节中的定义，则该对象是一个 代理特殊对象。这些内部方法在
| 内部方法 | 处理程序方法 |
|---|---|
| [[GetPrototypeOf]] |
getPrototypeOf
|
| [[SetPrototypeOf]] |
setPrototypeOf
|
| [[IsExtensible]] |
isExtensible
|
| [[PreventExtensions]] |
preventExtensions
|
| [[GetOwnProperty]] |
getOwnPropertyDescriptor
|
| [[DefineOwnProperty]] |
defineProperty
|
| [[HasProperty]] |
has
|
| [[Get]] |
get
|
| [[Set]] |
set
|
| [[Delete]] |
deleteProperty
|
| [[OwnPropertyKeys]] |
ownKeys
|
| [[Call]] |
apply
|
| [[Construct]] |
construct
|
当调用处理程序方法来提供代理对象内部方法的实现时，处理程序方法会将代理的目标对象作为参数传递。代理的处理程序对象不一定具有与每个基本内部方法对应的方法。如果处理程序对象没有对应于内部陷阱的方法，则在代理上调用内部方法将导致调用代理目标对象上的相应内部方法。
代理对象的 [[ProxyHandler]] 和 [[ProxyTarget]]
内部插槽在对象创建时总是被初始化，并且通常不可修改。有些代理对象是以允许其随后被撤销的方式创建的。当代理被撤销时，其 [[ProxyHandler]]
和 [[ProxyTarget]] 内部插槽被设置为
由于代理对象允许内部方法的实现由任意 ECMAScript 代码提供，因此可能会定义一个其处理程序方法违反
在以下算法描述中，假设 O 是一个 ECMAScript 代理对象，P 是一个
10.5.1 [[GetPrototypeOf]] ( )
[[GetPrototypeOf]] 内部方法的
- 执行 ?
ValidateNonRevokedProxy (O)。 - 设 target 为 O.[[ProxyTarget]]。
- 设 handler 为 O.[[ProxyHandler]]。
断言 ： handler 是一个对象 。- 设 trap 为 ?
GetMethod (handler,"getPrototypeOf" )。 - 如果 trap 是
undefined ，则：- 返回 ? target.[[GetPrototypeOf]]()。
- 设 handlerProto 为 ?
Call (trap, handler, « target »)。 - 如果 handlerProto 不是一个
对象 并且 handlerProto 不是null ，则抛出TypeError 异常。 - 设 extensibleTarget 为 ?
IsExtensible (target)。 - 如果 extensibleTarget 是
true ，则返回 handlerProto。 - 设 targetProto 为 ? target.[[GetPrototypeOf]]()。
- 如果
SameValue (handlerProto, targetProto) 是false ，则抛出TypeError 异常。 - 返回 handlerProto。
Proxy 对象的 [[GetPrototypeOf]] 强制执行以下不变量：
- [[GetPrototypeOf]] 的结果必须是一个对象或
null 。 - 如果目标对象不可扩展，则应用于代理对象的 [[GetPrototypeOf]] 必须返回与应用于代理对象的目标对象的 [[GetPrototypeOf]] 相同的值。
10.5.2 [[SetPrototypeOf]] ( V )
[[SetPrototypeOf]] 内部方法的
- 执行 ?
ValidateNonRevokedProxy (O)。 - 设 target 为 O.[[ProxyTarget]]。
- 设 handler 为 O.[[ProxyHandler]]。
断言 ： handler 是一个对象 。- 设 trap 为 ?
GetMethod (handler,"setPrototypeOf" )。 - 如果 trap 是
undefined ，则：- 返回 ? target.[[SetPrototypeOf]](V)。
- 设 booleanTrapResult 为
ToBoolean (?Call (trap, handler, « target, V »))。 - 如果 booleanTrapResult 是
false ，则返回false 。 - 设 extensibleTarget 为 ?
IsExtensible (target)。 - 如果 extensibleTarget 是
true ，则返回true 。 - 设 targetProto 为 ? target.[[GetPrototypeOf]]()。
- 如果
SameValue (V, targetProto) 是false ，则抛出TypeError 异常。 - 返回
true 。
Proxy 对象的 [[SetPrototypeOf]] 强制执行以下不变量：
- [[SetPrototypeOf]] 的结果是一个布尔值。
- 如果目标对象不可扩展，则参数值必须与应用于目标对象的 [[GetPrototypeOf]] 的结果相同。
10.5.3 [[IsExtensible]] ( )
[[IsExtensible]] 内部方法的
- 执行 ?
ValidateNonRevokedProxy (O)。 - 设 target 为 O.[[ProxyTarget]]。
- 设 handler 为 O.[[ProxyHandler]]。
断言 ：handler 是一个对象 。- 设 trap 为 ?
GetMethod (handler,"isExtensible" )。 - 如果 trap 是
undefined ，则：- 返回 ?
IsExtensible (target)。
- 返回 ?
- 设 booleanTrapResult 为
ToBoolean (?Call (trap, handler, « target »))。 - 设 targetResult 为 ?
IsExtensible (target)。 - 如果 booleanTrapResult 不等于 targetResult，则抛出
TypeError 异常。 - 返回 booleanTrapResult。
Proxy 对象的 [[IsExtensible]] 强制执行以下不变量：
- [[IsExtensible]] 的结果是一个布尔值。
- 应用于 Proxy 对象的 [[IsExtensible]] 必须返回与应用于 Proxy 对象的目标对象相同的参数值相同的结果。
10.5.4 [[PreventExtensions]] ( )
[[PreventExtensions]] 内部方法的
- 执行 ?
ValidateNonRevokedProxy (O)。 - 设 target 为 O.[[ProxyTarget]]。
- 设 handler 为 O.[[ProxyHandler]]。
断言 ：handler 是一个对象 。- 设 trap 为 ?
GetMethod (handler,"preventExtensions" )。 - 如果 trap 是
undefined ，则：- 返回 ? target.[[PreventExtensions]]()。
- 设 booleanTrapResult 为
ToBoolean (?Call (trap, handler, « target »))。 - 如果 booleanTrapResult 是
true ，则：- 设 extensibleTarget 为 ?
IsExtensible (target)。 - 如果 extensibleTarget 是
true ，抛出TypeError 异常。
- 设 extensibleTarget 为 ?
- 返回 booleanTrapResult。
Proxy 对象的 [[PreventExtensions]] 强制执行以下不变量：
- [[PreventExtensions]] 的结果是一个布尔值。
- 应用于 Proxy 对象的 [[PreventExtensions]] 仅当应用于 Proxy 对象的目标对象的 [[IsExtensible]] 结果为
false 时，才会返回true 。
10.5.5 [[GetOwnProperty]] ( P )
[[GetOwnProperty]] 内部方法的
-
执行 ?
ValidateNonRevokedProxy (O)。 - 设 target 为 O.[[ProxyTarget]]。
- 设 handler 为 O.[[ProxyHandler]]。
-
断言 ：handler 是一个对象 。 -
设 trap 为 ?
GetMethod (handler,"getOwnPropertyDescriptor" )。 - 如果 trap 是
undefined ，则：- 返回 ? target.[[GetOwnProperty]](P)。
-
设 trapResultObj 为 ?
Call (trap, handler, «target, P »)。 -
如果 trapResultObj 不是一个
对象 且 trapResultObj 不是undefined ，抛出一个TypeError 异常。 - 设 targetDesc 为 ? target.[[GetOwnProperty]](P)。
- 如果 trapResultObj 是
undefined ，则：-
如果 targetDesc 是
undefined ，返回undefined 。 -
如果 targetDesc.[[Configurable]] 是
false ，抛出一个TypeError 异常。 -
设 extensibleTarget 为 ?
IsExtensible (target)。 -
如果 extensibleTarget 是
false ，抛出一个TypeError 异常。 - 返回
undefined 。
-
如果 targetDesc 是
- 设 extensibleTarget 为 ?
IsExtensible (target)。 - 设 resultDesc 为 ?
ToPropertyDescriptor (trapResultObj)。 - 执行
CompletePropertyDescriptor (resultDesc)。 - 设 valid 为
IsCompatiblePropertyDescriptor (extensibleTarget, resultDesc, targetDesc)。 - 如果 valid 是
false ，抛出一个TypeError 异常。 - 如果 resultDesc.[[Configurable]] 是
false ，则：-
如果 targetDesc 是
undefined 或 targetDesc.[[Configurable]] 是true ，则：- 抛出一个
TypeError 异常。
- 抛出一个
- 如果 resultDesc 有一个 [[Writable]] 字段并且 resultDesc.[[Writable]] 是
false ，则：-
断言 ：targetDesc 有一个 [[Writable]] 字段。 -
如果 targetDesc.[[Writable]] 是
true ，抛出一个TypeError 异常。
-
-
如果 targetDesc 是
- 返回 resultDesc。
Proxy 对象的 [[GetOwnProperty]] 强制执行以下不变量：
-
[[GetOwnProperty]] 的结果必须是一个对象或
undefined 。 - 如果目标对象作为自身不可配置的属性存在，则该属性不能被报告为不存在。
- 如果目标对象作为自身不可扩展的属性存在，则该属性不能被报告为不存在。
- 如果目标对象是不可扩展的，且该属性不存在于目标对象的自身属性中，则该属性不能被报告为存在。
- 除非目标对象的自身不可配置属性存在，否则该属性不能被报告为不可配置。
- 除非目标对象的自身不可配置且不可写的属性存在，否则该属性不能被报告为既不可配置又不可写。
10.5.6 [[DefineOwnProperty]] ( P, Desc )
[[DefineOwnProperty]] 内部方法的
-
执行 ?
ValidateNonRevokedProxy (O)。 - 设 target 为 O.[[ProxyTarget]]。
- 设 handler 为 O.[[ProxyHandler]]。
-
断言 ：handler 是一个对象 。 -
设 trap 为 ?
GetMethod (handler,"defineProperty" )。 - 如果 trap 是
undefined ，则：- 返回 ? target.[[DefineOwnProperty]](P, Desc)。
-
设 descObj 为 ?
FromPropertyDescriptor (Desc)。 -
设 booleanTrapResult 为
ToBoolean (?Call (trap, handler, «target, P, descObj »))。 - 如果 booleanTrapResult 是
false ，返回false 。 - 设 targetDesc 为 ? target.[[GetOwnProperty]](P)。
-
设 extensibleTarget 为 ?
IsExtensible (target)。 - 如果 Desc 有一个 [[Configurable]] 字段且 Desc.[[Configurable]] 是
false ，则：-
设 settingConfigFalse 为
true 。
-
设 settingConfigFalse 为
- 否则，
-
设 settingConfigFalse 为
false 。
-
设 settingConfigFalse 为
- 如果 targetDesc 是
undefined ，则：- 如果 extensibleTarget 是
false ，抛出一个TypeError 异常。 - 如果 settingConfigFalse 是
true ，抛出一个TypeError 异常。
- 如果 extensibleTarget 是
- 否则，
-
如果
IsCompatiblePropertyDescriptor (extensibleTarget, Desc, targetDesc) 是false ，抛出一个TypeError 异常。 - 如果 settingConfigFalse 是
true 且 targetDesc.[[Configurable]] 是true ，抛出一个TypeError 异常。 - 如果
IsDataDescriptor (targetDesc) 是true ，targetDesc.[[Configurable]] 是false ，且 targetDesc.[[Writable]] 是true ，则：- 如果 Desc 有一个 [[Writable]] 字段且 Desc.[[Writable]] 是
false ，抛出一个TypeError 异常。
- 如果 Desc 有一个 [[Writable]] 字段且 Desc.[[Writable]] 是
-
如果
- 返回
true 。
Proxy 对象的 [[DefineOwnProperty]] 强制执行以下不变量：
- [[DefineOwnProperty]] 的结果是一个布尔值。
- 如果目标对象是不可扩展的，则不能添加属性。
- 除非目标对象存在相应的不可配置自身属性，否则属性不能是不可配置的。
- 除非目标对象存在相应的不可配置且不可写的自身属性，否则不可配置的属性不能是不可写的。
- 如果属性有相应的目标对象属性，则使用属性的属性描述符应用于目标对象的 [[DefineOwnProperty]] 不会抛出异常。
10.5.7 [[HasProperty]] ( P )
[[HasProperty]] 内部方法的
-
执行 ?
ValidateNonRevokedProxy (O)。 - 设 target 为 O.[[ProxyTarget]]。
- 设 handler 为 O.[[ProxyHandler]]。
-
断言 ：handler 是一个对象 。 -
设 trap 为 ?
GetMethod (handler,"has" )。 - 如果 trap 是
undefined ，则：- 返回 ? target.[[HasProperty]](P)。
-
设 booleanTrapResult 为
ToBoolean (?Call (trap, handler, «target, P »))。 - 如果 booleanTrapResult 是
false ，则：- 设 targetDesc 为 ? target.[[GetOwnProperty]](P)。
- 如果 targetDesc 不是
undefined ，则：-
如果 targetDesc.[[Configurable]] 是
false ，抛出一个TypeError 异常。 -
设 extensibleTarget 为 ?
IsExtensible (target)。 -
如果 extensibleTarget 是
false ，抛出一个TypeError 异常。
-
如果 targetDesc.[[Configurable]] 是
- 返回 booleanTrapResult。
Proxy 对象的 [[HasProperty]] 强制执行以下不变量：
- [[HasProperty]] 的结果是一个布尔值。
- 如果属性作为目标对象的不可配置自身属性存在，则不能报告该属性不存在。
- 如果属性作为目标对象的自身属性存在且目标对象不可扩展，则不能报告该属性不存在。
10.5.8 [[Get]] ( P, Receiver )
[[Get]] 内部方法的
-
执行 ?
ValidateNonRevokedProxy (O)。 - 设 target 为 O.[[ProxyTarget]]。
- 设 handler 为 O.[[ProxyHandler]]。
-
断言 ：handler 是一个对象 。 -
设 trap 为 ?
GetMethod (handler,"get" )。 - 如果 trap 是
undefined ，则：- 返回 ? target.[[Get]](P, Receiver)。
-
设 trapResult 为 ?
Call (trap, handler, «target, P, Receiver ») 。 - 设 targetDesc 为 ? target.[[GetOwnProperty]](P)。
- 如果 targetDesc 不是
undefined 且 targetDesc.[[Configurable]] 是false ，则：-
如果
IsDataDescriptor (targetDesc) 是true 且 targetDesc.[[Writable]] 是false ，则：-
如果
SameValue (trapResult, targetDesc.[[Value]]) 是false ，抛出一个TypeError 异常。
-
如果
-
如果
IsAccessorDescriptor (targetDesc) 是true 且 targetDesc.[[Get]] 是 undefined ，则：- 如果 trapResult 不是
undefined ，抛出一个TypeError 异常。
- 如果 trapResult 不是
-
如果
- 返回 trapResult。
10.5.9 [[Set]] ( P, V, Receiver )
[[Set]] 内部方法的
-
执行 ?
ValidateNonRevokedProxy (O)。 - 设 target 为 O.[[ProxyTarget]]。
- 设 handler 为 O.[[ProxyHandler]]。
-
断言 ：handler 是一个对象 。 -
设 trap 为 ?
GetMethod (handler,"set" )。 - 如果 trap 是
undefined ，则：- 返回 ? target.[[Set]](P, V, Receiver)。
-
设 booleanTrapResult 为
ToBoolean (?Call (trap, handler, «target, P, V, Receiver »))。 - 如果 booleanTrapResult 是
false ，返回false 。 - 设 targetDesc 为 ? target.[[GetOwnProperty]](P)。
- 如果 targetDesc 不是
undefined 且 targetDesc.[[Configurable]] 是false ，则：-
如果
IsDataDescriptor (targetDesc) 是true 且 targetDesc.[[Writable]] 是 false ，则：-
如果
SameValue (V, targetDesc.[[Value]]) 是false ，抛出一个TypeError 异常。
-
如果
-
如果
IsAccessorDescriptor (targetDesc) 是true，则： -
如果 targetDesc.[[Set]] 是
undefined ，抛出一个TypeError 异常。
-
如果 targetDesc.[[Set]] 是
-
如果
- 返回
true 。
10.5.10 [[Delete]] ( P )
[[Delete]] 内部方法的
-
执行 ?
ValidateNonRevokedProxy (O)。 - 设 target 为 O.[[ProxyTarget]]。
- 设 handler 为 O.[[ProxyHandler]]。
-
断言 ：handler 是一个对象 。 -
设 trap 为 ?
GetMethod (handler,"deleteProperty" )。 - 如果 trap 是
undefined ，则：- 返回 ? target.[[Delete]](P)。
-
设 booleanTrapResult 为
ToBoolean (?Call (trap, handler, «target, P »))。 - 如果 booleanTrapResult 是
false ，返回false 。 - 设 targetDesc 为 ? target.[[GetOwnProperty]](P)。
- 如果 targetDesc 是
undefined ，返回true 。 - 如果 targetDesc.[[Configurable]] 是
false ，抛出一个TypeError 异常。 -
设 extensibleTarget 为 ?
IsExtensible (target)。 - 如果 extensibleTarget 是
false ，抛出一个TypeError 异常。 - 返回
true 。
Proxy 对象的 [[Delete]] 强制执行以下不变量：
- [[Delete]] 的结果是一个布尔值。
- 如果目标对象存在一个不可配置的自身属性，则不能将其报告为已删除。
- 如果目标对象存在一个自身属性且目标对象是不可扩展的，则不能将其报告为已删除。
10.5.11 [[OwnPropertyKeys]] ( )
[[OwnPropertyKeys]] 内部方法的
-
执行 ?
ValidateNonRevokedProxy (O)。 - 设 target 为 O.[[ProxyTarget]]。
- 设 handler 为 O.[[ProxyHandler]]。
-
断言 ：handler 是一个对象 。 -
设 trap 为 ?
GetMethod (handler,"ownKeys" )。 - 如果 trap 是
undefined ，则：- 返回 ? target.[[OwnPropertyKeys]]()。
-
设 trapResultArray 为 ?
Call (trap, handler, «target »)。 -
设 trapResult 为 ?
CreateListFromArrayLike (trapResultArray, «String, Symbol »)。 - 如果 trapResult 包含任何重复项，抛出一个
TypeError 异常。 -
设 extensibleTarget 为 ?
IsExtensible (target)。 - 设 targetKeys 为 ? target.[[OwnPropertyKeys]]()。
-
断言 ：targetKeys 是一个包含列表 的属性键 。 -
断言 ：targetKeys 不包含重复项。 -
设 targetConfigurableKeys 为一个新的空
列表 。 -
设 targetNonconfigurableKeys 为一个新的空
列表 。 - 对于 targetKeys 的每个元素 key，执行以下步骤：
- 设 desc 为 ? target.[[GetOwnProperty]](key)。
- 如果 desc 不是
undefined 且 desc.[[Configurable]] 是false ，则：- 将 key 追加到 targetNonconfigurableKeys。
- 否则：
- 将 key 追加到 targetConfigurableKeys。
- 如果 extensibleTarget 是
true 且 targetNonconfigurableKeys 为空，则：- 返回 trapResult。
-
设 uncheckedResultKeys 为一个包含 trapResult 元素的
列表 。 - 对于 targetNonconfigurableKeys 的每个元素 key，执行以下步骤：
- 如果 uncheckedResultKeys 不包含 key，抛出一个
TypeError 异常。 - 从 uncheckedResultKeys 中移除 key。
- 如果 uncheckedResultKeys 不包含 key，抛出一个
- 如果 extensibleTarget 是
true ，返回 trapResult。 - 对于 targetConfigurableKeys 的每个元素 key，执行以下步骤：
- 如果 uncheckedResultKeys 不包含 key，抛出一个
TypeError 异常。 - 从 uncheckedResultKeys 中移除 key。
- 如果 uncheckedResultKeys 不包含 key，抛出一个
- 如果 uncheckedResultKeys 不为空，抛出一个
TypeError 异常。 - 返回 trapResult。
10.5.12 [[Call]] ( thisArgument, argumentsList )
[[Call]] 内部方法用于
- 执行 ?
ValidateNonRevokedProxy (O). - 让 target 等于 O.[[ProxyTarget]].
- 让 handler 等于 O.[[ProxyHandler]].
断言 : handler 是一个对象。- 让 trap 等于 ?
GetMethod (handler, "apply"). - 如果 trap 是 undefined，则
- 返回 ?
Call (target, thisArgument, argumentsList).
- 返回 ?
- 让 argArray 等于
CreateArrayFromList (argumentsList). - 返回 ?
Call (trap, handler, « target, thisArgument, argArray »).
10.5.13 [[Construct]] ( argumentsList, newTarget )
[[Construct]] 内部方法用于
- 执行 ?
ValidateNonRevokedProxy (O). - 让 target 等于 O.[[ProxyTarget]].
断言 :IsConstructor (target) 为 true。- 让 handler 等于 O.[[ProxyHandler]].
断言 : handler 是一个对象。- 让 trap 等于 ?
GetMethod (handler, "construct"). - 如果 trap 是 undefined，则
- 返回 ?
Construct (target, argumentsList, newTarget).
- 返回 ?
- 让 argArray 等于
CreateArrayFromList (argumentsList). - 让 newObj 等于 ?
Call (trap, handler, « target, argArray, newTarget »). - 如果 newObj 不是一个对象，抛出一个 TypeError 异常。
- 返回 newObj.
[[Construct]] 对于 Proxy 对象强制执行以下不变量：
- [[Construct]] 的结果必须是一个对象。
10.5.14 ValidateNonRevokedProxy ( proxy )
抽象操作 ValidateNonRevokedProxy 接受参数 proxy（一个
- 如果 proxy.[[ProxyTarget]] 是
null ，抛出TypeError 异常。 断言 : proxy.[[ProxyHandler]] 不是null 。- 返回
unused 。
10.5.15 ProxyCreate ( target, handler )
抽象操作 ProxyCreate 接受参数 target（一个
- 如果 target
不是一个对象 ，抛出TypeError 异常。 - 如果 handler
不是一个对象 ，抛出TypeError 异常。 - 让 P 等于
MakeBasicObject (« [[ProxyHandler]], [[ProxyTarget]] »)。 - 设置 P 的基本内部方法，除了 [[Call]] 和 [[Construct]]，按照
10.5 中的定义。 - 如果
IsCallable (target) 为true ，则- 设置 P.[[Call]]，如
10.5.12 中所述。 - 如果
IsConstructor (target) 为true ，则- 设置 P.[[Construct]]，如
10.5.13 中所述。
- 设置 P.[[Construct]]，如
- 设置 P.[[Call]]，如
- 设置 P.[[ProxyTarget]] 为 target。
- 设置 P.[[ProxyHandler]] 为 handler。
- 返回 P。
11 ECMAScript 语言：源代码
11.1 源代码
语法
ECMAScript 源代码 是一系列 Unicode 代码点。在 ECMAScript 语法允许的地方，所有从 U+0000 到 U+10FFFF 的 Unicode
代码点值，包括代理代码点，都可以出现在 ECMAScript 源代码中。用于存储和交换 ECMAScript 源代码的实际编码与本规范无关。不论外部源代码编码如何，符合规范的 ECMAScript
实现都将源代码处理为等效的
组合字符序列的组成部分被视为单独的 Unicode 代码点，即使用户可能将整个序列视为一个字符。
在字符串字面量、正则表达式字面量、模板字面量和标识符中，任何 Unicode 代码点也可以使用 Unicode 转义序列来表示，显式表达代码点的数值。在注释中，这样的转义序列实际上被忽略，作为注释的一部分。
ECMAScript 与 Java 编程语言在 Unicode 转义序列的行为上有所不同。例如，在 Java 程序中，如果 Unicode 转义序列 \u000A
出现在单行注释中，它会被解释为行终止符（Unicode 代码点 U+000A 是换行符（LF）），因此下一个代码点不再是注释的一部分。同样，如果 Unicode 转义序列 \u000A
出现在 Java 程序的字符串字面量中，它也会被解释为行终止符，字符串字面量中不允许有行终止符——必须写成 \n 而不是
\u000A，以使换行符（LF）成为字符串字面量的字符串值的一部分。在 ECMAScript 程序中，出现在注释中的 Unicode 转义序列从不被解释，因此不能终止注释。同样，出现在
ECMAScript 程序的字符串字面量中的 Unicode 转义序列始终是字面量的一部分，永远不会被解释为行终止符或可能终止字符串字面量的代码点。
11.1.1 静态语义: UTF16EncodeCodePoint ( cp )
抽象操作 UTF16EncodeCodePoint 接受参数 cp（一个 Unicode 代码点）并返回一个字符串。调用时，它执行以下步骤：
11.1.2 静态语义: CodePointsToString ( text )
抽象操作 CodePointsToString 接受参数 text（一个 Unicode 代码点序列）并返回一个字符串。它将 text 转换为字符串值，如
- 令 result 为空字符串。
- 对于 text 中的每个代码点 cp，执行以下步骤
- 将 result 设为
字符串连接 result 和UTF16EncodeCodePoint (cp) 的结果。
- 将 result 设为
- 返回 result。
11.1.3 静态语义: UTF16SurrogatePairToCodePoint ( lead, trail )
抽象操作 UTF16SurrogatePairToCodePoint 接受参数 lead（一个代码单元）和 trail（一个代码单元），并返回一个代码点。形成
UTF-16
11.1.4 静态语义: CodePointAt ( string, position )
抽象操作 CodePointAt 接受参数 string（一个字符串）和 position（一个非负
- 令 size 为 string 的长度。
断言 : position ≥ 0 并且 position < size。- 令 first 为 string 内索引 position 处的代码单元。
- 令 cp 为数值为 first 的代码点。
- 如果 first 既不是
前导代理项 也不是尾随代理项 ，则- 返回
记录 { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]:false }。
- 返回
- 如果 first 是
尾随代理项 或者 position + 1 = size，则- 返回
记录 { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]:true }。
- 返回
- 令 second 为 string 内索引 position + 1 处的代码单元。
- 如果 second 不是
尾随代理项 ，则- 返回
记录 { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]:true }。
- 返回
- 将 cp 设置为
UTF16SurrogatePairToCodePoint (first, second)。 - 返回
记录 { [[CodePoint]]: cp, [[CodeUnitCount]]: 2, [[IsUnpairedSurrogate]]:false }。
11.1.5 静态语义: StringToCodePoints ( string )
抽象操作 StringToCodePoints 接受参数 string（一个字符串）并返回一个代码点的
- 令 codePoints 为一个新的空的
列表 。 - 令 size 为 string 的长度。
- 令 position 为 0。
- 重复，当 position 小于 size 时，
- 令 cp 为
CodePointAt (string, position)。 - 将 cp.[[CodePoint]] 添加到 codePoints。
- 将 position 设置为 position + cp.[[CodeUnitCount]]。
- 令 cp 为
- 返回 codePoints。
11.1.6 静态语义: ParseText ( sourceText, goalSymbol )
抽象操作 ParseText 接受参数 sourceText（一个 Unicode 代码点序列）和 goalSymbol（ECMAScript
语法中的一个非终结符）并返回一个
另见第
11.2 Types of Source Code
有四种类型的 ECMAScript 代码：
-
Global code 是被当作 ECMAScript
Script 处理的源文本。特定Script 的 global code 不包括任何被解析为FunctionDeclaration 、FunctionExpression 、GeneratorDeclaration 、GeneratorExpression 、AsyncFunctionDeclaration 、AsyncFunctionExpression 、AsyncGeneratorDeclaration 、AsyncGeneratorExpression 、MethodDefinition 、ArrowFunction 、AsyncArrowFunction 、ClassDeclaration 或ClassExpression 的任何源文本。 -
Eval code 是传递给内建
eval函数的源文本。更准确地说，如果传递给内建eval函数的参数是一个字符串 ，它被当作 ECMAScriptScript 处理。特定调用eval的 eval code 是该Script 的 global code 部分。 -
Function code 是解析为 ECMAScript
function object 的 [[ECMAScriptCode]] 和 [[FormalParameters]] 内部槽的源文本（见10.2 ）。特定 ECMAScript 函数的 function code 不包括作为嵌套函数的 function code 解析的任何源文本，如FunctionDeclaration 、FunctionExpression 、GeneratorDeclaration 、GeneratorExpression 、AsyncFunctionDeclaration 、AsyncFunctionExpression 、AsyncGeneratorDeclaration 、AsyncGeneratorExpression 、MethodDefinition 、ArrowFunction 、AsyncArrowFunction 、ClassDeclaration 或ClassExpression 。 -
Module code 是提供为
ModuleBody 的源文本。它是在模块初始化时直接执行的代码。特定模块的 module code 不包括作为嵌套FunctionDeclaration 、FunctionExpression 、GeneratorDeclaration 、GeneratorExpression 、AsyncFunctionDeclaration 、AsyncFunctionExpression 、AsyncGeneratorDeclaration 、AsyncGeneratorExpression 、MethodDefinition 、ArrowFunction 、AsyncArrowFunction 、ClassDeclaration 或ClassExpression 的任何源文本。
Function code 通常以函数定义的主体形式提供（
将
11.2.1 指令序言和 "use strict" 指令
指令序言 是出现在
"use strict" 指令 是出现在
"use strict" 或 'use strict'。
11.2.2 严格模式代码
ECMAScript 语法单元可以使用无限制或严格模式语法和语义进行处理
(
-
全局代码 是严格模式代码，如果它以包含"use strict" 指令 的指令序言 开始。 -
模块代码 总是严格模式代码。 -
ClassDeclaration 或ClassExpression 的所有部分都是严格模式代码。 -
Eval 代码 是严格模式代码，如果它以包含"use strict" 指令 的指令序言 开始，或者调用eval是包含在严格模式代码中的直接 eval 。 -
函数代码 是严格模式代码， 如果相关的FunctionDeclaration ，FunctionExpression ，GeneratorDeclaration ，GeneratorExpression ，AsyncFunctionDeclaration ，AsyncFunctionExpression ，AsyncGeneratorDeclaration ，AsyncGeneratorExpression ，MethodDefinition ，ArrowFunction ， 或AsyncArrowFunction 包含在严格模式代码中， 或者如果生成函数的 [[ECMAScriptCode]] 内部槽的代码以包含"use strict" 指令 的指令序言 开始。 -
提供给内置 Function，Generator，AsyncFunction 和 AsyncGenerator
构造函数 的函数代码 是严格模式代码， 如果最后一个参数是一个字符串 ，当处理时它是一个以 包含"use strict" 指令 的指令序言 开始的函数体 。
不是严格模式代码的 ECMAScript 代码称为 非严格代码。
11.2.3 非 ECMAScript 函数
ECMAScript 实现可能支持对函数
12 ECMAScript 语言：词法语法
ECMAScript
在多个情况下，词法输入元素的识别对消耗输入元素的语法语境是敏感的。这需要词法语法的多个
语法
12.1 Unicode 格式控制字符
Unicode 格式控制字符（即 Unicode 字符数据库中类别为 “Cf” 的字符，如左到右标记或右到左标记）是用于在缺乏高级协议（如标记语言）的情况下控制一段文本格式的控制代码。
允许在源文本中使用格式控制字符以便于编辑和显示是很有用的。所有格式控制字符都可以在注释、字符串字面量、模板字面量和正则表达式字面量中使用。
U+200C（零宽非连接符）和 U+200D（零宽连接符）是用于在某些语言中形成单词或短语时进行必要区分的格式控制字符。在
U+FEFF（零宽不换行空格）是主要用于文本开头的格式控制字符，用来标记它为 Unicode 并允许检测文本的编码和字节顺序。出于这种目的而使用的 <ZWNBSP>
字符有时也会出现在文本的开头之后，例如由于文件连接的结果。在
某些格式控制字符在注释、字符串字面量和正则表达式字面量之外的特殊处理在
| 代码点 | 名称 | 缩写 | 用法 |
|---|---|---|---|
U+200C
|
零宽非连接符 | <ZWNJ> |
|
U+200D
|
零宽连接符 | <ZWJ> |
|
U+FEFF
|
零宽不换行空格 | <ZWNBSP> |
|
12.2 空白符
空白符代码点用于提高源文本的可读性，并将词法单元（不可分割的词法单位）彼此分开，但除此之外没有其他意义。空白符代码点可以出现在任意两个词法单元之间，以及输入的开头或结尾。空白符代码点可以出现在
ECMAScript 的空白符代码点列在
| 代码点 | 名称 | 缩写 |
|---|---|---|
U+0009 |
CHARACTER TABULATION | <TAB> |
U+000B |
LINE TABULATION | <VT> |
U+000C |
FORM FEED (FF) | <FF> |
U+FEFF |
ZERO WIDTH NO-BREAK SPACE | <ZWNBSP> |
| general category 中的任意代码点 “Space_Separator” | <USP> |
U+0020 (SPACE) 和 U+00A0 (NO-BREAK SPACE) 代码点是 <USP> 的一部分。
除了表
语法
12.3 行终止符
像空白符代码点一样，行终止符代码点用于提高源文本的可读性，并将词法单元（不可分割的词法单位）彼此分开。然而，与空白符代码点不同，行终止符对语法规则的行为有一定影响。通常，行终止符可以出现在任意两个词法单元之间，但在某些地方，语法规则禁止它们的出现。行终止符还会影响自动分号插入的过程（
行终止符可以出现在
行终止符包含在正则表达式中的 \s 类匹配的空白符代码点集合中。
ECMAScript 行终止符代码点列在
| 代码点 | Unicode 名称 | 缩写 |
|---|---|---|
U+000A |
LINE FEED (LF) | <LF> |
U+000D |
CARRIAGE RETURN (CR) | <CR> |
U+2028 |
LINE SEPARATOR | <LS> |
U+2029 |
PARAGRAPH SEPARATOR | <PS> |
只有表
语法
12.4 注释
注释可以是单行或多行。多行注释不能嵌套。
由于单行注释可以包含任何 Unicode 代码点，除了 // 标记到行尾的所有代码点组成。然而，行尾的
注释表现得像空白符，并被丢弃，除了如果一个
语法
本节中的一些规则在
12.5 Hashbang 注释
Hashbang 注释是位置敏感的，并且像其他类型的注释一样，从语法解析的输入元素流中被丢弃。
语法
12.6 词法单元(Tokens)
语法
12.7 名称和关键字
本标准指定了特定的代码点添加：U+0024 (美元符号) 和 U+005F (下划线) 在
语法
非终结符
_。
具有 Unicode 属性 “ID_Start” 和 “ID_Continue” 的代码点集合分别包括具有 Unicode 属性 “Other_ID_Start” 和 “Other_ID_Continue” 的代码点。
12.7.1 标识符名称
在 \ 不贡献任何代码点。Unicode 转义序列不能用于对
根据 Unicode 标准，两个规范等效的
12.7.1.1 静态语义：早期错误
-
如果
IdentifierCodePoint 不属于由IdentifierStartChar 派生的某个 Unicode 代码点，则这是一个语法错误。
-
如果
IdentifierCodePoint 不属于由IdentifierPartChar 派生的某个 Unicode 代码点，则这是一个语法错误。
12.7.1.2 静态语义：IdentifierCodePoints
语法导向操作
- 让 cp 为
IdentifierCodePoint 的IdentifierStart 。 - 返回 « cp »。
- 让 cps 为
IdentifierCodePoints 派生出的IdentifierName 。 - 让 cp 为
IdentifierCodePoint 的IdentifierPart 。 - 返回
列表串联 的 cps 和 « cp »。
12.7.1.3 静态语义：IdentifierCodePoint
语法导向操作
- 返回
IdentifierStartChar 匹配的代码点。
- 返回
IdentifierPartChar 匹配的代码点。
- 返回数值为
Hex4Digits 的代码点。
- 返回数值为
CodePoint 的代码点。
12.7.2 关键字和保留字
关键字 是一个与
if、while、async、await 等。
保留字 是一个不能用作标识符的
if 和 while 是保留字，await
仅在异步函数和模块中是保留的，而 async 不是保留的，它可以在变量名或语句标签中使用。
本规范使用语法生成式和
await 和 yield，都是无条件保留的。await 和 yield 的例外情况在
-
那些始终允许作为标识符使用的，不是关键字的名称，例如
Math、window、toString和_; -
那些永远不允许作为标识符使用的名称，即下面列出的
ReservedWord （除了await和yield）; -
那些在特定上下文中允许作为标识符使用的名称，即
await和yield; -
那些在
严格模式代码 中上下文不允许作为标识符使用的名称：let、static、implements、interface、package、private、protected和public; -
那些始终允许作为标识符使用，但在某些语法生成式中的某些地方也出现为关键字的名称，即
Identifier 不允许：as、async、from、get、meta、of、set和target。
术语 条件关键字 或 上下文关键字 有时用来指在上述最后三类中的关键字，这些关键字可以在某些上下文中作为标识符使用，而在其他上下文中作为关键字使用。
语法
根据
\ Unicode 转义序列表示。
\
els\u{65} 来声明一个名为 "else" 的变量。
enum 目前在本规范中不作为关键字使用。它是一个 未来保留字，为将来的语言扩展预留。
同样，implements、interface、package、private、protected
和 public 在
12.8 标点符号
语法
12.9 字面量
12.9.1 Null 字面量
语法
12.9.2 布尔字面量
语法
12.9.3 数值字面量
语法
紧跟在
例如：3in 是错误的，而不是两个输入元素 3 和 in。
12.9.3.1 静态语义：早期错误
- 如果
此产生式匹配的源文本 是严格模式代码 ，则会产生语法错误。
12.9.3.2 静态语义：MV
数值字面量表示
-
DecimalLiteral :: DecimalIntegerLiteral . DecimalDigits DecimalIntegerLiteral 的 MV 加上 (DecimalDigits 的 MV × 10 -n )，其中 n 是DecimalDigits 中的代码点数，排除所有NumericLiteralSeparator 的出现。 -
DecimalLiteral :: DecimalIntegerLiteral . ExponentPart DecimalIntegerLiteral 的 MV × 10 e，其中 e 是ExponentPart 的 MV。 -
DecimalLiteral :: DecimalIntegerLiteral . DecimalDigits ExponentPart DecimalIntegerLiteral 的 MV 加上 (DecimalDigits 的 MV × 10 -n ) ) × 10 e，其中 n 是DecimalDigits 中的代码点数，排除所有NumericLiteralSeparator 的出现，e 是ExponentPart 的 MV。 -
DecimalLiteral :: . DecimalDigits DecimalDigits 的 MV × 10 -n，其中 n 是DecimalDigits 中的代码点数，排除所有NumericLiteralSeparator 的出现。 -
DecimalLiteral :: . DecimalDigits ExponentPart DecimalDigits 的 MV × 10 e - n ，其中 n 是DecimalDigits 中的代码点数，排除所有NumericLiteralSeparator 的出现，e 是ExponentPart 的 MV。 -
DecimalLiteral :: DecimalIntegerLiteral ExponentPart DecimalIntegerLiteral 的 MV × 10 e，其中 e 是ExponentPart 的 MV。 -
DecimalIntegerLiteral :: 0 -
DecimalIntegerLiteral :: NonZeroDigit NumericLiteralSeparator opt DecimalDigits NonZeroDigit 的 MV × 10 n ) 加上DecimalDigits 的 MV，其中 n 是DecimalDigits 中的代码点数，排除所有NumericLiteralSeparator 的出现。 -
DecimalDigits :: DecimalDigits DecimalDigit DecimalDigits 的 MV × 10 ) 加上DecimalDigit 的 MV。 -
DecimalDigits :: DecimalDigits NumericLiteralSeparator DecimalDigit DecimalDigits 的 MV × 10 ) 加上DecimalDigit 的 MV。 -
ExponentPart :: ExponentIndicator SignedInteger SignedInteger 的 MV。 -
SignedInteger :: - DecimalDigits DecimalDigits 的负值。 -
DecimalDigit :: 0 HexDigit :: 0 OctalDigit :: 0 LegacyOctalEscapeSequence :: 0 BinaryDigit :: 0 -
DecimalDigit :: 1 NonZeroDigit :: 1 HexDigit :: 1 OctalDigit :: 1 BinaryDigit :: 1 -
DecimalDigit :: 2 NonZeroDigit :: 2 HexDigit :: 2 OctalDigit :: 2 -
DecimalDigit :: 3 NonZeroDigit :: 3 HexDigit :: 3 OctalDigit :: 3 -
DecimalDigit :: 4 NonZeroDigit :: 4 HexDigit :: 4 OctalDigit :: 4 -
DecimalDigit :: 5 NonZeroDigit :: 5 HexDigit :: 5 OctalDigit :: 5 -
DecimalDigit :: 6 NonZeroDigit :: 6 HexDigit :: 6 OctalDigit :: 6 -
DecimalDigit :: 7 NonZeroDigit :: 7 HexDigit :: 7 OctalDigit :: 7 -
DecimalDigit :: 8 NonZeroDigit :: 8 NonOctalDigit :: 8 HexDigit :: 8 -
DecimalDigit :: 9 NonZeroDigit :: 9 NonOctalDigit :: 9 HexDigit :: 9 -
HexDigit :: a HexDigit :: A -
HexDigit :: b HexDigit :: B -
HexDigit :: c HexDigit :: C -
HexDigit :: d HexDigit :: D -
HexDigit :: e HexDigit :: E -
HexDigit :: f HexDigit :: F -
BinaryDigits :: BinaryDigits BinaryDigit BinaryDigits 的 MV × 2 ) 加上BinaryDigit 的 MV。 -
BinaryDigits :: BinaryDigits NumericLiteralSeparator BinaryDigit BinaryDigits 的 MV × 2 ) 加上BinaryDigit 的 MV。 -
OctalDigits :: OctalDigits OctalDigit OctalDigits 的 MV × 8 ) 加上OctalDigit 的 MV。 -
OctalDigits :: OctalDigits NumericLiteralSeparator OctalDigit OctalDigits 的 MV × 8 ) 加上OctalDigit 的 MV。 -
LegacyOctalIntegerLiteral :: LegacyOctalIntegerLiteral OctalDigit LegacyOctalIntegerLiteral 的 MV × 8 ) 加上OctalDigit 的 MV。 -
NonOctalDecimalIntegerLiteral :: LegacyOctalLikeDecimalIntegerLiteral NonOctalDigit LegacyOctalLikeDecimalIntegerLiteral 的 MV × 10 ) 加上NonOctalDigit 的 MV。 -
NonOctalDecimalIntegerLiteral :: NonOctalDecimalIntegerLiteral DecimalDigit NonOctalDecimalIntegerLiteral 的 MV × 10 ) 加上DecimalDigit 的 MV。 -
LegacyOctalLikeDecimalIntegerLiteral :: LegacyOctalLikeDecimalIntegerLiteral OctalDigit LegacyOctalLikeDecimalIntegerLiteral 的 MV × 10 ) 加上OctalDigit 的 MV。 -
HexDigits :: HexDigits HexDigit HexDigits 的 MV × 16 ) 加上HexDigit 的 MV。 -
HexDigits :: HexDigits NumericLiteralSeparator HexDigit HexDigits 的 MV × 16 ) 加上HexDigit 的 MV。
12.9.3.3 静态语义：NumericValue
- 返回
RoundMVResult (DecimalLiteral 的 MV)。
- 返回
𝔽 (NonDecimalIntegerLiteral 的 MV)。
- 返回
𝔽 (LegacyOctalIntegerLiteral 的 MV)。
- 返回
BigInt 值 的 MVNonDecimalIntegerLiteral 。
- 返回
0 ℤ。
- 返回
BigInt 值 的 MVNonZeroDigit 。
- 让 n 为
DecimalDigits 中代码点的数量，排除所有NumericLiteralSeparator 的出现。 - 让 mv 为 (
NonZeroDigit 的 MV × 10n) 加上DecimalDigits 的 MV。 - 返回
ℤ (mv)。
12.9.4 字符串字面量
字符串字面量是用单引号或双引号括起来的 0 个或更多 Unicode 代码点。Unicode 代码点也可以通过转义序列表示。除了闭合引号的代码点、U+005C（反斜杠）、U+000D（回车符）和
U+000A（换行符）外，所有代码点都可以直接出现在字符串字面量中。任何代码点都可以以转义序列的形式出现。字符串字面量求值为 ECMAScript 字符串值。在生成这些字符串值时，Unicode 代码点按照
语法
非终结符
<LF> 和 <CR> 不能出现在字符串字面量中，除非作为 \n 或 \u000A。
12.9.4.1 静态语义：早期错误
- 如果
此产生式匹配的源文本 是严格模式代码 ，则这是一个语法错误。
12.9.4.2 静态语义：SV
字符串字面量表示
-
StringLiteral :: " " -
StringLiteral :: ' ' -
DoubleStringCharacters :: DoubleStringCharacter DoubleStringCharacters 字符串连接 的 SVDoubleStringCharacter 和DoubleStringCharacters 。 -
SingleStringCharacters :: SingleStringCharacter SingleStringCharacters 字符串连接 的 SVSingleStringCharacter 和SingleStringCharacters 。 -
DoubleStringCharacter :: SourceCharacter 但不能是 " 或\ 或LineTerminator 之一UTF16EncodeCodePoint 的结果。 -
DoubleStringCharacter :: <LS> -
DoubleStringCharacter :: <PS> -
DoubleStringCharacter :: LineContinuation -
SingleStringCharacter :: SourceCharacter 但不能是 ' 或\ 或LineTerminator 之一UTF16EncodeCodePoint 的结果。 -
SingleStringCharacter :: <LS> -
SingleStringCharacter :: <PS> -
SingleStringCharacter :: LineContinuation -
EscapeSequence :: 0 -
CharacterEscapeSequence :: SingleEscapeCharacter SingleEscapeCharacter 根据表 38 确定。
| 转义序列 | 代码单元值 | Unicode 字符名称 | 符号 |
|---|---|---|---|
\b |
0x0008 |
退格符 | <BS> |
\t |
0x0009 |
字符制表符 | <HT> |
\n |
0x000A |
换行符 (LF) | <LF> |
\v |
0x000B |
行制表符 | <VT> |
\f |
0x000C |
换页符 (FF) | <FF> |
\r |
0x000D |
回车符 (CR) | <CR> |
\" |
0x0022 |
引号 | " |
\' |
0x0027 |
撇号 | ' |
\\ |
0x005C |
反斜杠 | \ |
-
NonEscapeCharacter :: SourceCharacter 但不能是 EscapeCharacter 或LineTerminator 之一UTF16EncodeCodePoint 的结果。 -
EscapeSequence :: LegacyOctalEscapeSequence LegacyOctalEscapeSequence 的 MV。 -
NonOctalDecimalEscapeSequence :: 8 -
NonOctalDecimalEscapeSequence :: 9 -
HexEscapeSequence :: x HexDigit HexDigit HexEscapeSequence 的 MV。 -
Hex4Digits :: HexDigit HexDigit HexDigit HexDigit Hex4Digits 的 MV。 -
UnicodeEscapeSequence :: u{ CodePoint } CodePoint 的 MV 执行UTF16EncodeCodePoint 的结果。 -
TemplateEscapeSequence :: 0
12.9.4.3 静态语义：MV
-
LegacyOctalEscapeSequence :: ZeroToThree OctalDigit ZeroToThree 的 MV) 加上OctalDigit 的 MV。 -
LegacyOctalEscapeSequence :: FourToSeven OctalDigit FourToSeven 的 MV) 加上OctalDigit 的 MV。 -
LegacyOctalEscapeSequence :: ZeroToThree OctalDigit OctalDigit ZeroToThree 的 MV) 加上 (8 倍的第一个OctalDigit 的 MV) 加上第二个OctalDigit 的 MV。 -
ZeroToThree :: 0 -
ZeroToThree :: 1 -
ZeroToThree :: 2 -
ZeroToThree :: 3 -
FourToSeven :: 4 -
FourToSeven :: 5 -
FourToSeven :: 6 -
FourToSeven :: 7 -
HexEscapeSequence :: x HexDigit HexDigit HexDigit 的 MV) 加上第二个HexDigit 的 MV。 -
Hex4Digits :: HexDigit HexDigit HexDigit HexDigit HexDigit 的 MV) 加上 (0x100 倍的第二个HexDigit 的 MV) 加上 (0x10 倍的第三个HexDigit 的 MV) 加上第四个HexDigit 的 MV。
12.9.5 正则表达式字面量
下面的生成式描述了正则表达式字面量的语法，并由输入元素扫描器用于查找正则表达式字面量的结束位置。包含
实现可以扩展
语法
正则表达式字面量不能为空；而不是表示一个空的正则表达式字面量，代码单元序列 // 启动一个单行注释。要指定一个空的正则表达式，请使用：/(?:)/。
12.9.5.1 静态语义：BodyText
- 返回被识别为
RegularExpressionBody 的源文本。
12.9.5.2 静态语义：FlagText
- 返回被识别为
RegularExpressionFlags 的源文本。
12.9.6 模板字面量词法组件
语法
12.9.6.1 静态语义：TV
-
NoSubstitutionTemplate :: ` ` -
TemplateHead :: ` ${ -
TemplateMiddle :: } ${ -
TemplateTail :: } ` -
TemplateCharacters :: TemplateCharacter TemplateCharacters undefined ，如果TemplateCharacter 的 TV 是undefined 或TemplateCharacters 的 TV 是undefined 。否则，它是字符串连接 的 TVTemplateCharacter 和 TVTemplateCharacters 。 -
TemplateCharacter :: SourceCharacter 但不包括 ` 或\ 或$ 或LineTerminator SourceCharacter 匹配的代码点执行UTF16EncodeCodePoint 的结果。 -
TemplateCharacter :: $ -
TemplateCharacter :: \ TemplateEscapeSequence SV TemplateEscapeSequence 。 -
TemplateCharacter :: \ NotEscapeSequence undefined 。 -
TemplateCharacter :: LineTerminatorSequence TRV LineTerminatorSequence 。 -
LineContinuation :: \ LineTerminatorSequence
12.9.6.2 静态语义：TRV
-
NoSubstitutionTemplate :: ` ` -
TemplateHead :: ` ${ -
TemplateMiddle :: } ${ -
TemplateTail :: } ` -
TemplateCharacters :: TemplateCharacter TemplateCharacters 字符串连接 的 TRVTemplateCharacter 和 TRVTemplateCharacters 。 -
TemplateCharacter :: SourceCharacter 但不包括 ` 或\ 或$ 或LineTerminator SourceCharacter 匹配的代码点执行UTF16EncodeCodePoint 的结果。 -
TemplateCharacter :: $ -
TemplateCharacter :: \ TemplateEscapeSequence 字符串连接 的代码单元 0x005C（反斜杠）和TemplateEscapeSequence 的 TRV。 -
TemplateCharacter :: \ NotEscapeSequence 字符串连接 的代码单元 0x005C（反斜杠）和NotEscapeSequence 的 TRV。 -
TemplateEscapeSequence :: 0 -
NotEscapeSequence :: 0 DecimalDigit 字符串连接 的代码单元 0x0030（数字零）和DecimalDigit 的 TRV。 -
NotEscapeSequence :: x [lookahead ∉ HexDigit ] -
NotEscapeSequence :: x HexDigit [lookahead ∉ HexDigit ]字符串连接 的代码单元 0x0078（拉丁字母小写 x）和HexDigit 的 TRV。 -
NotEscapeSequence :: u [lookahead ∉ HexDigit ][lookahead ≠ { ] -
NotEscapeSequence :: u HexDigit [lookahead ∉ HexDigit ]字符串连接 的代码单元 0x0075（拉丁字母小写 u）和HexDigit 的 TRV。 -
NotEscapeSequence :: u HexDigit HexDigit [lookahead ∉ HexDigit ]字符串连接 的代码单元 0x0075（拉丁字母小写 u）、第一个HexDigit 的 TRV 和第二个HexDigit 的 TRV。 -
NotEscapeSequence :: u HexDigit HexDigit HexDigit [lookahead ∉ HexDigit ]字符串连接 的代码单元 0x0075（拉丁字母小写 u）、第一个HexDigit 的 TRV、第二个HexDigit 的 TRV 和第三个HexDigit 的 TRV。 -
NotEscapeSequence :: u { [lookahead ∉ HexDigit ]字符串连接 的代码单元 0x0075（拉丁字母小写 u）和代码单元 0x007B（左花括号）。 -
NotEscapeSequence :: u { NotCodePoint [lookahead ∉ HexDigit ]字符串连接 的代码单元 0x0075（拉丁字母小写 u）、代码单元 0x007B（左花括号）和NotCodePoint 的 TRV。 -
NotEscapeSequence :: u { CodePoint [lookahead ∉ HexDigit ][lookahead ≠ } ]字符串连接 的代码单元 0x0075（拉丁字母小写 u）、代码单元 0x007B（左花括号）和CodePoint 的 TRV。 -
DecimalDigit :: 之一 0 1 2 3 4 5 6 7 8 9 UTF16EncodeCodePoint 的结果。 -
CharacterEscapeSequence :: NonEscapeCharacter SV NonEscapeCharacter 。 -
SingleEscapeCharacter :: 之一 ' " \ b f n r t v UTF16EncodeCodePoint 的结果。 -
HexEscapeSequence :: x HexDigit HexDigit 字符串连接 的代码单元 0x0078（拉丁字母小写 x）、第一个HexDigit 的 TRV 和第二个HexDigit 的 TRV。 -
UnicodeEscapeSequence :: u Hex4Digits 字符串连接 的代码单元 0x0075（拉丁字母小写 u）和Hex4Digits 的 TRV。 -
UnicodeEscapeSequence :: u{ CodePoint } 字符串连接 的代码单元 0x0075（拉丁字母小写 u）、代码单元 0x007B（左花括号）、CodePoint 的 TRV 和代码单元 0x007D（右花括号）。 -
Hex4Digits :: HexDigit HexDigit HexDigit HexDigit 字符串连接 的第一个HexDigit 的 TRV、第二个HexDigit 的 TRV、第三个HexDigit 的 TRV 和第四个HexDigit 的 TRV。 -
HexDigits :: HexDigits HexDigit 字符串连接 的HexDigits 的 TRV 和HexDigit 的 TRV。 -
HexDigit :: 之一 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F UTF16EncodeCodePoint 的结果。 -
LineContinuation :: \ LineTerminatorSequence 字符串连接 的代码单元 0x005C（反斜杠）和LineTerminatorSequence 的 TRV。 -
LineTerminatorSequence :: <LF> -
LineTerminatorSequence :: <CR> -
LineTerminatorSequence :: <LS> -
LineTerminatorSequence :: <PS> -
LineTerminatorSequence :: <CR> <LF>
12.10 自动分号插入
大多数 ECMAScript 语句和声明必须以分号结尾。这些分号总是可以显式出现在源代码中。然而，为了方便，在某些情况下，这些分号可以从源代码中省略。在这些情况下，可以通过描述分号自动插入到源代码令牌流中的那些情况来解释。
12.10.1 自动分号插入规则
在以下规则中，“令牌”是指使用当前词法
分号插入有三条基本规则：
-
当从左到右解析源文本时，遇到不允许的令牌（称为冒犯令牌）时，如果以下条件之一为真， 则会在冒犯令牌之前自动插入分号：
- 当从左到右解析源文本时，遇到输入令牌流的结尾并且解析器无法将输入令牌流解析为目标非终结符的单个实例时， 则在输入流的结尾自动插入分号。
- 当从左到右解析源文本时，遇到某些语法规则允许的令牌，但该语法规则是受限规则，并且该令牌是紧跟在标注
“[no
行终止符 here]”之后的受限规则中的第一个令牌 （因此称为受限令牌），并且受限令牌与前一个令牌之间至少有一个行终止符 分隔时， 则在受限令牌之前自动插入分号。
但是，前述规则有一个额外的优先条件：如果分号将被解析为空语句或成为for语句头中的两个分号之一，
则不会自动插入分号（见
以下是语法中唯一的受限规则：
这些受限规则的实际效果如下：
- 当遇到
++或--令牌且解析器将其视为后缀操作符，并且前一个令牌与++或--令牌之间至少有一个行终止符 时， 则在++或--令牌之前自动插入分号。 - 当遇到
continue、break、return、throw或yield令牌并且在下一个令牌之前遇到一个行终止符 时， 则在continue、break、return、throw或yield令牌之后自动插入分号。 - 当箭头函数的参数之后有一个
行终止符 且在=>令牌之前时，自动插入分号并且标点符号会导致语法错误。 - 当
async令牌之后有一个行终止符 且在function或标识符名称 或(令牌之前时，自动插入分号并且async令牌不会被视为与后续令牌相同的表达式或类元素。 - 当
async令牌之后有一个行终止符 且在*令牌之前时，自动插入分号并且标点符号会导致语法错误。
因此，对ECMAScript程序员的实际建议是：
12.10.2 自动分号插入的示例
本节为非规范性内容。以下源代码
{ 1 2 } 3即使使用自动分号插入规则，也不是 ECMAScript 语法中的有效句子。相反，以下源代码
{ 1
2 } 3也不是有效的 ECMAScript 句子，但通过自动分号插入会被转换为以下内容：
{ 1
;2 ;} 3;这是一个有效的 ECMAScript 句子。
以下源代码
for (a; b
)不是有效的 ECMAScript 句子，且不会因自动分号插入而改变，因为 for 语句头部需要的分号。自动分号插入永远不会插入 for 语句头部的两个分号之一。
以下源代码
return
a + b通过自动分号插入会被转换为以下内容：
return;
a + b;表达式 a + b 不会被视为 return 语句要返回的值，因为 return 与 a + b
之间有一个
以下源代码
a = b
++c通过自动分号插入会被转换为以下内容：
a = b;
++c;符号 ++ 不会被视为应用于变量 b 的后缀运算符，因为 b 与 ++ 之间有一个
以下源代码
if (a > b)
else c = d不是有效的 ECMAScript 句子，且即使在 else 符号之前没有任何语法规则适用，自动分号插入也不会改变，因为自动插入的分号会被解析为一个空语句。
以下源代码
a = b + c
(d + e).print()不会被自动分号插入规则改变，因为第二行开始的括号表达式可以被解释为函数调用的参数列表：
a = b + c(d + e).print()在赋值语句必须以左括号开始的情况下，程序员最好在前一条语句的末尾提供一个显式分号，而不是依赖自动分号插入。
12.10.3 自动分号插入的有趣案例
本节为非规范性内容。ECMAScript 程序可以通过依赖自动分号插入来以很少分号的风格编写。如上所述，分号并不会在每个换行处插入，自动分号插入可能依赖跨行终止符的多个标记。
随着新的语法特性被添加到 ECMAScript 中，可能会增加一些语法产生式，这会导致依赖自动分号插入的行在解析时改变语法产生式。
在本节的目的中，如果某个地方的分号是否插入取决于之前的源文本，则该自动分号插入的案例被认为是有趣的。本节的其余部分描述了 ECMAScript 这一版本中一些有趣的自动分号插入案例。
12.10.3.1 语句列表中自动分号插入的有趣案例
在一个
- 开括号 (
()。没有分号，这两行会被视为一个CallExpression 。 - 开方括号 (
[)。没有分号，这两行会被视为属性访问，而不是一个ArrayLiteral 或ArrayAssignmentPattern 。 - 模板字符串 (
`)。没有分号，这两行会被解释为一个标记模板 (13.3.11 )，前一个表达式作为MemberExpression 。 - 一元
+或-。没有分号，这两行会被解释为使用对应的二元运算符。 - 正则表达式文字。没有分号，这两行可能会被解析为
/MultiplicativeOperator ，例如如果正则表达式有标志。
12.10.3.2 自动分号插入和“[无 行终止符 这里]”的案例
本节为非规范性内容。
ECMAScript 包含一些语法产生式，它们包括“[无
本节的其余部分描述了 ECMAScript 这一版本中使用“[无
12.10.3.2.1 带有可选操作数和“[无 行终止符 这里]”的语法产生式列表
UpdateExpression 。ContinueStatement 。BreakStatement 。ReturnStatement 。YieldExpression 。- 异步函数定义 (
15.8 ) 与函数定义 (15.2 ) 相关。
13 ECMAScript 语言：表达式
13.1 标识符
语法
yield 和 await 在语法中允许作为
let
await 0;13.1.1 静态语义：早期错误
-
如果
由该生成式匹配的源文本 包含在严格模式代码 中，并且StringValue 的Identifier 是"arguments" 或"eval" ，那么这是一个语法错误。
-
如果
由该生成式匹配的源文本 包含在严格模式代码 中，那么这是一个语法错误。
- 如果该生成式有一个 [Yield] 参数，那么这是一个语法错误。
- 如果该生成式有一个 [Await] 参数，那么这是一个语法错误。
-
如果该生成式有一个 [Yield] 参数，并且
StringValue 的Identifier 是"yield" ，那么这是一个语法错误。 -
如果该生成式有一个 [Await] 参数，并且
StringValue 的Identifier 是"await" ，那么这是一个语法错误。
-
如果这个短语包含在
严格模式代码 中，并且StringValue 的IdentifierName 是"implements" 、"interface" 、"let" 、"package" 、"private" 、"protected" 、"public" 、"static" 或"yield" ，那么这是一个语法错误。 -
如果语法的
目标符号 是Module ，并且StringValue 的IdentifierName 是"await" ，那么这是一个语法错误。 -
如果
StringValue 的IdentifierName 是任何ReservedWord 的StringValue ，除了yield或await，那么这是一个语法错误。
13.1.2 静态语义：StringValue
- 让 idTextUnescaped 为
IdentifierCodePoints 的IdentifierName 。 - 返回
CodePointsToString (idTextUnescaped)。
- 返回
"yield" 。
- 返回
"await" 。
- 返回
StringValue 的IdentifierName 。
- 返回 0x0023（数字符号）和
StringValue 的IdentifierName 的字符串连接 。
- 返回
SV 的StringLiteral 。
13.1.3 运行时语义：评估
-
返回 ?
ResolveBinding (StringValue 的Identifier )。
-
返回 ?
ResolveBinding ("yield" )。
-
返回 ?
ResolveBinding ("await" )。
评估
在 yield
可以用作标识符。评估 yield 解析为
13.2 主要表达式
语法
补充语法
当处理如下产生式实例时
对
13.2.1 this 关键字
13.2.1.1 运行时语义：求值
- 返回 ?
ResolveThisBinding ().
13.2.2 标识符引用
关于
13.2.3 字面量
语法
13.2.3.1 运行时语义：求值
- 返回
null 。
- 如果
BooleanLiteral 是标记false，返回false 。 - 如果
BooleanLiteral 是标记true，返回true 。
- 返回
NumericValue 的NumericLiteral ，如12.9.3 中定义。
- 返回
SV 的StringLiteral ，如12.9.4.2 中定义。
13.2.4 数组初始化器
数组元素可以在元素列表的开头、中间或结尾省略。每当元素列表中的逗号前没有
语法
13.2.4.1 运行时语义：数组积累
- 返回 ?
ArrayAccumulation ofElision with arguments array and (nextIndex + 1)。
- 如果
Elision 存在，则- 设置 nextIndex 为 ?
ArrayAccumulation ofElision with arguments array and nextIndex。
- 设置 nextIndex 为 ?
- 令 initResult 为 ?
Evaluation ofAssignmentExpression 。 - 令 initValue 为 ?
GetValue (initResult)。 - 执行 !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (nextIndex)), initValue)。 - 返回 nextIndex + 1。
- 如果
Elision 存在，则- 设置 nextIndex 为 ?
ArrayAccumulation ofElision with arguments array and nextIndex。
- 设置 nextIndex 为 ?
- 返回 ?
ArrayAccumulation ofSpreadElement with arguments array and nextIndex。
- 令 spreadRef 为 ?
Evaluation ofAssignmentExpression 。 - 令 spreadObj 为 ?
GetValue (spreadRef)。 - 令 iteratorRecord 为 ?
GetIterator (spreadObj,sync )。 - 重复，
- 令 next 为 ?
IteratorStepValue (iteratorRecord)。 - 如果 next 为
done ，返回 nextIndex。 - 执行 !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (nextIndex)), next)。 - 设置 nextIndex 为 nextIndex + 1。
- 令 next 为 ?
13.2.4.2 运行时语义：求值
- 令 array 为 !
ArrayCreate (0)。 - 如果
Elision 存在，则- 执行 ?
ArrayAccumulation ofElision with arguments array and 0。
- 执行 ?
- 返回 array。
- 令 array 为 !
ArrayCreate (0)。 - 执行 ?
ArrayAccumulation ofElementList with arguments array and 0。 - 返回 array。
- 令 array 为 !
ArrayCreate (0)。 - 令 nextIndex 为 ?
ArrayAccumulation ofElementList with arguments array and 0。 - 如果
Elision 存在，则- 执行 ?
ArrayAccumulation ofElision with arguments array and nextIndex。
- 执行 ?
- 返回 array。
13.2.5 对象初始化器
对象初始化器是一个描述对象初始化的表达式，写成类似字面量的形式。它是一个由零个或多个
语法
在某些上下文中，
13.2.5.1 静态语义：早期错误
-
如果
HasDirectSuper ofMethodDefinition 是true ，则这是语法错误。 -
如果
PrivateBoundIdentifiers ofMethodDefinition 不为空，则这是语法错误。
除了描述实际的对象初始化器外，
- 如果任何源文本与此生产匹配，则这是语法错误。
此生产的存在是为了使
-
如果
PropertyNameList ofPropertyDefinitionList 包含任何__proto__的重复条目，并且这些条目中至少有两个是从PropertyDefinition : PropertyName : AssignmentExpression ObjectLiteral 包含在Script 中，并且正在为JSON.parse解析（请参阅JSON.parse 的步骤4 ），则不适用此规则。
由
13.2.5.2 静态语义：IsComputedPropertyKey
- 返回
false 。
- 返回
true 。
13.2.5.3 静态语义：PropertyNameList
- 让propName成为
PropName ofPropertyDefinition 。 - 如果propName是
empty ，则返回一个新的空列表 。 - 返回« propName »。
- 让list成为
PropertyNameList ofPropertyDefinitionList 。 - 让propName成为
PropName ofPropertyDefinition 。 - 如果propName是
empty ，则返回list。 - 返回
列表连接 of list和« propName »。
13.2.5.4 运行时语义：求值
- 让obj成为
OrdinaryObjectCreate (%Object.prototype% )。 - 对
PropertyDefinitionList 执行PropertyDefinitionEvaluation ，参数为obj。 - 返回obj。
- 返回
StringValue ofIdentifierName 。
- 返回
SV ofStringLiteral 。
- 让nbr成为
NumericValue ofNumericLiteral 。 - 返回!
ToString (nbr)。
- 让exprValue成为
Evaluation ofAssignmentExpression 。 - 让propName成为
GetValue (exprValue)。 - 返回
ToPropertyKey (propName)。
13.2.5.5 运行时语义：PropertyDefinitionEvaluation
- 对
PropertyDefinitionList 执行PropertyDefinitionEvaluation ，参数为object。 - 对
PropertyDefinition 执行PropertyDefinitionEvaluation ，参数为object。 - 返回
unused 。
- 让exprValue成为
Evaluation ofAssignmentExpression 。 - 让fromValue成为
GetValue (exprValue)。 - 让excludedNames成为一个新的空
列表 。 - 对object、fromValue和excludedNames执行
CopyDataProperties 。 - 返回
unused 。
- 让propName成为
StringValue ofIdentifierReference 。 - 让exprValue成为
Evaluation ofIdentifierReference 。 - 让propValue成为
GetValue (exprValue)。 断言 ：object是一个普通的、可扩展的对象，没有不可配置的属性。- 对object、propName和propValue执行
CreateDataPropertyOrThrow 。 - 返回
unused 。
- 让propKey成为
Evaluation ofPropertyName 。 - 如果此
PropertyDefinition 包含在一个Script 中，并且正在为JSON.parse求值（请参阅7 ofJSON.parse ），则- 让isProtoSetter成为
false 。
- 让isProtoSetter成为
- 否则，如果propKey是__proto__并且
IsComputedPropertyKey ofPropertyName 是false ，则- 让isProtoSetter成为
true 。
- 让isProtoSetter成为
- 否则，
- 让isProtoSetter成为
false 。
- 让isProtoSetter成为
- 如果
IsAnonymousFunctionDefinition ofAssignmentExpression 是true 并且isProtoSetter是false ，则- 让propValue成为
NamedEvaluation ofAssignmentExpression with argument propKey。
- 让propValue成为
- 否则，
- 让exprValueRef成为
Evaluation ofAssignmentExpression 。 - 让propValue成为
GetValue (exprValueRef)。
- 让exprValueRef成为
- 如果isProtoSetter是
true ，则- 如果propValue是
一个对象 或propValue是null，则- 执行!object.[[SetPrototypeOf]](propValue)。
- 返回
unused 。
- 如果propValue是
断言 ：object是一个普通的、可扩展的对象，没有不可配置的属性。- 对object、propKey和propValue执行
CreateDataPropertyOrThrow 。 - 返回
unused 。
- 对
MethodDefinition 执行MethodDefinitionEvaluation ，参数为object和true 。 - 返回
unused 。
13.2.6 函数定义表达式
参见
参见
参见
13.2.7 正则表达式字面量
语法
参见
13.2.7.1 静态语义：早期错误
- 如果
IsValidRegularExpressionLiteral (RegularExpressionLiteral )为false ，则这是一个语法错误。
13.2.7.2 静态语义：IsValidRegularExpressionLiteral(literal)
抽象操作IsValidRegularExpressionLiteral接受参数literal（一个
- 令flags为
FlagText 的literal。 - 如果flags包含
d、g、i、m、s、u、v或y之外的任何代码点，或flags包含的任何代码点不止一次，则返回false 。 - 如果flags包含
u，则令u为true ；否则令u为false 。 - 如果flags包含
v，则令v为true ；否则令v为false 。 - 令patternText为
BodyText 的literal。 - 如果u为
false 且v为false ，则- 令stringValue为
CodePointsToString (patternText)。 - 将patternText设置为解释stringValue的每个16位元素为Unicode BMP代码点而得到的代码点序列。不对元素应用UTF-16解码。
- 令stringValue为
- 令parseResult为
ParsePattern (patternText, u, v)。 - 如果parseResult是一个
Parse Node ，则返回true ；否则返回false 。
13.2.7.3 运行时语义：求值
- 令pattern为
CodePointsToString (BodyText 的RegularExpressionLiteral )。 - 令flags为
CodePointsToString (FlagText 的RegularExpressionLiteral )。 - 返回!
RegExpCreate (pattern, flags)。
13.2.8 模板字面量
语法
13.2.8.1 静态语义: 早期错误
-
如果 [Tagged] 参数未设置，并且
NoSubstitutionTemplate Contains NotEscapeSequence ，则这是一个语法错误。
-
如果
TemplateStrings 的结果中元素的数量大于或等于 232，则这是一个语法错误。
-
如果 [Tagged] 参数未设置，并且
TemplateHead Contains NotEscapeSequence ，则这是一个语法错误。
-
如果 [Tagged] 参数未设置，并且
TemplateTail Contains NotEscapeSequence ，则这是一个语法错误。
-
如果 [Tagged] 参数未设置，并且
TemplateMiddle Contains NotEscapeSequence .
13.2.8.2 静态语义：模板字符串
模板字符串是一个
- 返回 «
TemplateString (NoSubstitutionTemplate , raw) ».
- 设 head 为 «
TemplateString (TemplateHead , raw) ». - 设 tail 为
TemplateStrings ofTemplateSpans with argument raw. - 返回 head 和 tail 的
列表连接 .
- 返回 «
TemplateString (TemplateTail , raw) ».
- 设 middle 为
TemplateStrings ofTemplateMiddleList with argument raw. - 设 tail 为 «
TemplateString (TemplateTail , raw) ». - 返回 middle 和 tail 的
列表连接 .
- 返回 «
TemplateString (TemplateMiddle , raw) ».
- 设 front 为
TemplateStrings ofTemplateMiddleList with argument raw. - 设 last 为 «
TemplateString (TemplateMiddle , raw) ». - 返回 front 和 last 的
列表连接 .
13.2.8.3 静态语义：TemplateString ( templateToken, raw )
抽象操作 TemplateString 接受参数 templateToken（一个
如果 raw 是
13.2.8.4 GetTemplateObject ( templateLiteral )
抽象操作 GetTemplateObject 接受参数 templateLiteral（一个
- 设 realm 为
当前领域记录 。 - 设 templateRegistry 为 realm.[[TemplateMap]]。
- 对于 templateRegistry 中的每个元素 e，执行
- 如果 e.[[Site]] 是
与 templateLiteral 相同的解析节点 ，则- 返回 e.[[Array]]。
- 如果 e.[[Site]] 是
- 设 rawStrings 为
TemplateStrings of templateLiteral with argumenttrue 。 断言 ：rawStrings 是一个字符串列表 。- 设 cookedStrings 为
TemplateStrings of templateLiteral with argumentfalse 。 - 设 count 为 cookedStrings 的元素数量。
断言 ：count ≤ 232 - 1。- 设 template 为 !
ArrayCreate (count)。 - 设 rawObj 为 !
ArrayCreate (count)。 - 设 index 为 0。
- 重复，当 index < count 时，
- 设 prop 为 !
ToString (𝔽 (index))。 - 设 cookedValue 为 cookedStrings[index]。
- 执行 !
DefinePropertyOrThrow (template, prop, PropertyDescriptor { [[Value]]: cookedValue, [[Writable]]:false , [[Enumerable]]:true , [[Configurable]]:false })。 - 设 rawValue 为字符串值 rawStrings[index]。
- 执行 !
DefinePropertyOrThrow (rawObj, prop, PropertyDescriptor { [[Value]]: rawValue, [[Writable]]:false , [[Enumerable]]:true , [[Configurable]]:false })。 - 设 index 为 index + 1。
- 设 prop 为 !
- 执行 !
SetIntegrityLevel (rawObj,frozen )。 - 执行 !
DefinePropertyOrThrow (template,"raw" , PropertyDescriptor { [[Value]]: rawObj, [[Writable]]:false , [[Enumerable]]:false , [[Configurable]]:false })。 - 执行 !
SetIntegrityLevel (template,frozen )。 - 将记录 { [[Site]]: templateLiteral, [[Array]]: template } 追加到 realm.[[TemplateMap]]。
- 返回 template。
模板对象的创建不会导致
程序代码中的每个
本规范的未来版本可能会定义模板对象的附加不可枚举属性。
13.2.8.5 运行时语义：SubstitutionEvaluation
SubstitutionEvaluation 是一个
- 返回一个新的空
列表 。
- 返回 ?
SubstitutionEvaluation ofTemplateMiddleList 。
- 设 subRef 为 ?
Evaluation ofExpression 。 - 设 sub 为 ?
GetValue (subRef)。 - 返回 « sub »。
- 设 preceding 为 ?
SubstitutionEvaluation ofTemplateMiddleList 。 - 设 nextRef 为 ?
Evaluation ofExpression 。 - 设 next 为 ?
GetValue (nextRef)。 - 返回 preceding 和 « next » 的
列表连接 。
13.2.8.6 运行时语义：求值
- 返回
NoSubstitutionTemplate 的TV ，定义在12.9.6 。
- 设 head 为
TemplateHead 的TV ，定义在12.9.6 。 - 设 subRef 为 ?
Evaluation ofExpression 。 - 设 sub 为 ?
GetValue (subRef)。 - 设 middle 为 ?
ToString (sub)。 - 设 tail 为 ?
Evaluation ofTemplateSpans 。 - 返回 head、middle 和 tail 的
字符串连接 。
String.prototype.concat 而不是 + 运算符。
- 返回
TemplateTail 的TV ，定义在12.9.6 。
- 设 head 为 ?
Evaluation ofTemplateMiddleList 。 - 设 tail 为
TemplateTail 的TV ，定义在12.9.6 。 - 返回 head 和 tail 的
字符串连接 。
- 设 head 为
TemplateMiddle 的TV ，定义在12.9.6 。 - 设 subRef 为 ?
Evaluation ofExpression 。 - 设 sub 为 ?
GetValue (subRef)。 - 设 middle 为 ?
ToString (sub)。 - 返回 head 和 middle 的
字符串连接 。
String.prototype.concat 而不是 + 运算符。
- 设 rest 为 ?
Evaluation ofTemplateMiddleList 。 - 设 middle 为
TemplateMiddle 的TV ，定义在12.9.6 。 - 设 subRef 为 ?
Evaluation ofExpression 。 - 设 sub 为 ?
GetValue (subRef)。 - 设 last 为 ?
ToString (sub)。 - 返回 rest、middle 和 last 的
字符串连接 。
String.prototype.concat 而不是 + 运算符。
13.2.9 分组运算符
13.2.9.1 静态语义：早期错误
13.2.9.2 运行时语义：求值
- 设 expr 为
ParenthesizedExpression 被覆盖 的CoverParenthesizedExpressionAndArrowParameterList 。 - 返回 ?
Evaluation of expr。
- 返回 ?
Evaluation ofExpression 。这可能是 Reference 类型。
此算法不会对 delete 和 typeof 等运算符应用于带括号的表达式。
13.3 左值表达式
语法
补充语法
当处理以下产生式的一个实例时
13.3.1 静态语义
13.3.1.1 静态语义：早期错误
- 如果任何源代码与此产生式匹配，则这是一个语法错误。
此产生式存在是为了防止自动分号插入规则（
a?.b
`c`以便将其解释为两个有效的语句。目的是保持与没有可选链的类似代码的一致性：
a.b
`c`这是一个有效的语句，并且自动分号插入不适用。
13.3.2 属性访问器
属性通过名称访问，使用点表示法：
或方括号表示法：
点表示法通过以下句法转换解释：
其行为与以下相同：
同样地：
其行为与以下相同：
其中 <identifier-name-string> 是评估
13.3.2.1 运行时语义：评估
- 设 baseReference 为 ?
Evaluation 的MemberExpression 。 - 设 baseValue 为 ?
GetValue (baseReference)。 - 如果
源代码匹配 此MemberExpression 是严格模式代码 ，设 strict 为true ；否则设 strict 为false 。 - 返回 ?
EvaluatePropertyAccessWithExpressionKey (baseValue,Expression , strict)。
- 设 baseReference 为 ?
Evaluation 的MemberExpression 。 - 设 baseValue 为 ?
GetValue (baseReference)。 - 如果
源代码匹配 此MemberExpression 是严格模式代码 ，设 strict 为true ；否则设 strict 为false 。 - 返回
EvaluatePropertyAccessWithIdentifierKey (baseValue,IdentifierName , strict)。
- 设 baseReference 为 ?
Evaluation 的MemberExpression 。 - 设 baseValue 为 ?
GetValue (baseReference)。 - 设 fieldNameString 为
StringValue 的PrivateIdentifier 。 - 返回
MakePrivateReference (baseValue, fieldNameString)。
- 设 baseReference 为 ?
Evaluation 的CallExpression 。 - 设 baseValue 为 ?
GetValue (baseReference)。 - 如果
源代码匹配 此CallExpression 是严格模式代码 ，设 strict 为true ；否则设 strict 为false 。 - 返回 ?
EvaluatePropertyAccessWithExpressionKey (baseValue,Expression , strict)。
- 设 baseReference 为 ?
Evaluation 的CallExpression 。 - 设 baseValue 为 ?
GetValue (baseReference)。 - 如果
源代码匹配 此CallExpression 是严格模式代码 ，设 strict 为true ；否则设 strict 为false 。 - 返回
EvaluatePropertyAccessWithIdentifierKey (baseValue,IdentifierName , strict)。
- 设 baseReference 为 ?
Evaluation 的CallExpression 。 - 设 baseValue 为 ?
GetValue (baseReference)。 - 设 fieldNameString 为
StringValue 的PrivateIdentifier 。 - 返回
MakePrivateReference (baseValue, fieldNameString)。
13.3.3 EvaluatePropertyAccessWithExpressionKey ( baseValue, expression, strict )
抽象操作 EvaluatePropertyAccessWithExpressionKey 接受参数 baseValue（一个
- 设 propertyNameReference 为 ?
Evaluation 的 expression。 - 设 propertyNameValue 为 ?
GetValue (propertyNameReference)。 - 设 propertyKey 为 ?
ToPropertyKey (propertyNameValue)。 - 返回
引用记录 { [[Base]]: baseValue, [[ReferencedName]]: propertyKey, [[Strict]]: strict, [[ThisValue]]:empty }。
13.3.4 EvaluatePropertyAccessWithIdentifierKey ( baseValue, identifierName, strict )
抽象操作 EvaluatePropertyAccessWithIdentifierKey 接受参数 baseValue（一个
- 设 propertyNameString 为
StringValue 的 identifierName。 - 返回
引用记录 { [[Base]]: baseValue, [[ReferencedName]]: propertyNameString, [[Strict]]: strict, [[ThisValue]]:empty }。
13.3.5 The new Operator
13.3.5.1 运行时语义：评估
- 返回 ?
EvaluateNew (NewExpression ,empty )。
- 返回 ?
EvaluateNew (MemberExpression ,Arguments )。
13.3.5.1.1 EvaluateNew ( constructExpr, arguments )
抽象操作 EvaluateNew 接受参数 constructExpr（一个
- 设 ref 为 ?
Evaluation 的 constructExpr。 - 设 constructor 为 ?
GetValue (ref)。 - 如果 arguments 是
empty ，- 设 argList 为一个新空的
列表 。
- 设 argList 为一个新空的
- 否则，
- 设 argList 为 ?
ArgumentListEvaluation 的 arguments。
- 设 argList 为 ?
- 如果
IsConstructor (constructor) isfalse ，抛出一个TypeError 异常。 - 返回 ?
Construct (constructor, argList)。
13.3.6 Function Calls
13.3.6.1 运行时语义：评估
- 设 expr 为
CallMemberExpression 被CoverCallExpressionAndAsyncArrowHead 覆盖的部分。 - 设 memberExpr 为 expr 的
MemberExpression 。 - 设 arguments 为 expr 的
Arguments 。 - 设 ref 为 ?
Evaluation 的 memberExpr。 - 设 func 为 ?
GetValue (ref)。 - 如果 ref 是一个
引用记录 ，IsPropertyReference (ref) 是false ，且 ref.[[ReferencedName]] 是"eval" ，则- 如果
SameValue (func,%eval% ) 是true ，则- 设 argList 为 ?
ArgumentListEvaluation 的 arguments。 - 如果 argList 没有元素，返回
undefined 。 - 设 evalArg 为 argList 的第一个元素。
- 如果
源代码匹配 此CallExpression 是严格模式代码 ，设 strictCaller 为true 。否则设 strictCaller 为false 。 - 返回
?
PerformEval (evalArg, strictCaller,true )。
- 设 argList 为 ?
- 如果
- 设 thisCall 为这个
CallExpression 。 - 设 tailCall 为
IsInTailPosition (thisCall)。 - 返回 ?
EvaluateCall (func, ref, arguments, tailCall)。
一个
- 设 ref 为 ?
Evaluation 的CallExpression 。 - 设 func 为 ?
GetValue (ref)。 - 设 thisCall 为这个
CallExpression 。 - 设 tailCall 为
IsInTailPosition (thisCall)。 - 返回 ?
EvaluateCall (func, ref,Arguments , tailCall)。
13.3.6.2 EvaluateCall ( func, ref, arguments, tailPosition )
抽象操作 EvaluateCall 接受参数 func（一个
- 如果 ref 是一个
引用记录 ，则- 如果
IsPropertyReference (ref) 是true ，则- 设 thisValue 为
GetThisValue (ref)。
- 设 thisValue 为
- 否则，
- 如果
- 否则，
- 设 thisValue 为
undefined 。
- 设 thisValue 为
- 设 argList 为 ?
ArgumentListEvaluation 的 arguments。 - 如果 func
不是一个对象 ，抛出一个TypeError 异常。 - 如果
IsCallable (func) 是false ，抛出一个TypeError 异常。 - 如果 tailPosition 是
true ， 执行PrepareForTailCall ()。 - 返回 ?
Call (func, thisValue, argList)。
13.3.7 The super 关键字
13.3.7.1 运行时语义：评估
- 设 env 为运行时执行上下文的
环境记录 。 - 设 home 为 env.GetSuperBase()。
- 设 propertyNameReference 为 ?
Evaluation 的表达式 。 - 设 propertyNameValue 为 ?
GetValue (propertyNameReference)。 - 设 propertyKey 为 ?
ToPropertyKey (propertyNameValue)。 - 设 strict 为
IsStrictReference (propertyNameReference)。 - 返回
MakeSuperPropertyReference (home, propertyKey, strict)。
- 设 env 为运行时执行上下文的
环境记录 。 - 设 home 为 env.GetSuperBase()。
- 设 strict 为
IsStrictReference (propertyNameReference)。 - 设 propertyKey 为
StringValue 的IdentifierName 。 - 返回
MakeSuperPropertyReference (home, propertyKey, strict)。
- 设 newTarget 为
GetNewTarget ()。 断言 ：newTarget是一个对象 。- 设 func 为
GetSuperConstructor ()。 - 设 argList 为 ?
ArgumentListEvaluation 的Arguments 。 - 如果
IsConstructor (func) 是false ，抛出一个TypeError 异常。 - 设 result 为 ?
Construct (func, argList, newTarget)。 - 设 thisER 为
GetThisEnvironment ()。 - 执行 ? thisER.BindThisValue(result)。
- 设 F 为 thisER.[[FunctionObject]]。
断言 ：F 是一个 ECMAScript函数对象 。- 执行 ?
InitializeInstanceElements (result, F)。 - 返回 result。
13.3.7.2 GetSuperConstructor ( )
抽象操作 GetSuperConstructor 不接受任何参数，并返回一个
- 设 envRec 为
GetThisEnvironment ()。 断言 ：envRec 是一个函数环境记录 。- 设 activeFunction 为 envRec.[[FunctionObject]]。
断言 ：activeFunction 是一个 ECMAScript函数对象 。- 设 superConstructor 为 ! activeFunction.[[GetPrototypeOf]]()。
- 返回 superConstructor。
13.3.7.3 MakeSuperPropertyReference ( actualThis, propertyKey, strict )
抽象操作 MakeSuperPropertyReference 接受参数 actualThis（一个
- 设 env 为
GetThisEnvironment ()。 断言 ： env.HasSuperBinding() 是true 。- 设 baseValue 为 ? env.GetSuperBase()。
- 返回
引用记录 { [[Base]]: baseValue, [[ReferencedName]]: propertyKey, [[Strict]]: strict, [[ThisValue]]: actualThis }。
13.3.8 参数列表
参数列表的评估产生一个
13.3.8.1 运行时语义：参数列表评估
语法导向操作
- 返回一个新的空
列表 。
- 设ref为?
AssignmentExpression的评估。 - 设arg为?
GetValue (ref)。 - 返回 « arg »。
- 设list为一个新空
列表 。 - 设spreadRef为?
AssignmentExpression的评估。 - 设spreadObj为?
GetValue (spreadRef)。 - 设iteratorRecord为?
GetIterator (spreadObj,sync )。 - 重复,
- 设next为?
IteratorStepValue (iteratorRecord)。 - 如果next是
done ，返回 list。 - 将next添加到list。
- 设next为?
- 设precedingArgs为?
ArgumentListEvaluation ofArgumentList 。 - 设ref为?
Evaluation ofAssignmentExpression 。 - 设arg为?
GetValue (ref)。 - 返回
列表连接 of precedingArgs 和 « arg »。
- 设precedingArgs为?
ArgumentListEvaluation ofArgumentList 。 - 设spreadRef为?
Evaluation ofAssignmentExpression 。 - 设iteratorRecord为?
GetIterator (?GetValue (spreadRef),sync )。 - 重复,
- 设next为?
IteratorStepValue (iteratorRecord)。 - 如果next是
done ，返回 precedingArgs。 - 将next添加到precedingArgs。
- 设next为?
- 设templateLiteral为这个
TemplateLiteral 。 - 设siteObj为
GetTemplateObject (templateLiteral)。 - 返回 « siteObj »。
- 设templateLiteral为这个
TemplateLiteral 。 - 设siteObj为
GetTemplateObject (templateLiteral)。 - 设remaining为?
ArgumentListEvaluation ofSubstitutionTemplate 。 - 返回
列表连接 of « siteObj » 和 remaining。
- 设firstSubRef为?
Evaluation ofExpression 。 - 设firstSub为?
GetValue (firstSubRef)。 - 设restSub为?
SubstitutionEvaluation ofTemplateSpans 。 断言 : restSub 是一个 可能为空的列表 。- 返回
列表连接 of « firstSub » 和 restSub。
13.3.9 可选链
?.标记开始。13.3.9.1 运行时语义：评估
- 设baseReference为?
Evaluation ofMemberExpression 。 - 设baseValue为?
GetValue (baseReference)。 - 如果baseValue是
undefined 或null ，则- 返回
undefined 。
- 返回
- 返回?
ChainEvaluation ofOptionalChain with arguments baseValue 和 baseReference。
- 设baseReference为?
Evaluation ofCallExpression 。 - 设baseValue为?
GetValue (baseReference)。 - 如果baseValue是
undefined 或null ，则- 返回
undefined 。
- 返回
- 返回?
ChainEvaluation ofOptionalChain with arguments baseValue 和 baseReference。
- 设baseReference为?
Evaluation ofOptionalExpression 。 - 设baseValue为?
GetValue (baseReference)。 - 如果baseValue是
undefined 或null ，则- 返回
undefined 。
- 返回
- 返回?
ChainEvaluation ofOptionalChain with arguments baseValue 和 baseReference。
13.3.9.2 运行时语义：链评估
语法导向操作
- 设thisChain为这个
OptionalChain 。 - 设tailCall为
IsInTailPosition (thisChain)。 - 返回?
EvaluateCall (baseValue, baseReference,Arguments , tailCall)。
- 如果这个
OptionalChain 的源文本匹配 是严格模式代码 ，设strict为true ；否则设strict为false 。 - 返回?
EvaluatePropertyAccessWithExpressionKey (baseValue,Expression , strict)。
- 如果这个
OptionalChain 的源文本匹配 是严格模式代码 ，设strict为true ；否则设strict为false 。 - 返回
EvaluatePropertyAccessWithIdentifierKey (baseValue,IdentifierName , strict)。
- 设fieldNameString为
PrivateIdentifier 的StringValue 。 - 返回
MakePrivateReference (baseValue, fieldNameString)。
- 设optionalChain为
OptionalChain 。 - 设newReference为?
ChainEvaluation of optionalChain with arguments baseValue 和 baseReference。 - 设newValue为?
GetValue (newReference)。 - 设thisChain为这个
OptionalChain 。 - 设tailCall为
IsInTailPosition (thisChain)。 - 返回?
EvaluateCall (newValue, newReference,Arguments , tailCall)。
- 设optionalChain为
OptionalChain 。 - 设newReference为?
ChainEvaluation of optionalChain with arguments baseValue 和 baseReference。 - 设newValue为?
GetValue (newReference)。 - 如果这个
OptionalChain 的源文本匹配 是严格模式代码 ，设strict为true ；否则设strict为false 。 - 返回?
EvaluatePropertyAccessWithExpressionKey (newValue,Expression , strict)。
- 设optionalChain为
OptionalChain 。 - 设newReference为?
ChainEvaluation of optionalChain with arguments baseValue 和 baseReference。 - 设newValue为?
GetValue (newReference)。 - 如果这个
OptionalChain 的源文本匹配 是严格模式代码 ，设strict为true ；否则设strict为false 。 - 返回
EvaluatePropertyAccessWithIdentifierKey (newValue,IdentifierName , strict)。
- 设optionalChain为
OptionalChain 。 - 设newReference为?
ChainEvaluation of optionalChain with arguments baseValue 和 baseReference。 - 设newValue为?
GetValue (newReference)。 - 设fieldNameString为
PrivateIdentifier 的StringValue 。 - 返回
MakePrivateReference (newValue, fieldNameString)。
13.3.10 Import 调用
13.3.10.1 运行时语义: Evaluation
- 设referrer为
GetActiveScriptOrModule ()。 - 如果referrer是
null ，设 referrer为当前领域记录 。 - 设argRef为?
Evaluation ofAssignmentExpression 。 - 设specifier为?
GetValue (argRef)。 - 设promiseCapability为!
NewPromiseCapability (%Promise% )。 - 设specifierString为
Completion (ToString (specifier))。 IfAbruptRejectPromise (specifierString, promiseCapability)。- 执行
HostLoadImportedModule (referrer, specifierString,empty , promiseCapability)。 - 返回promiseCapability.[[Promise]]。
13.3.10.1.1 ContinueDynamicImport ( promiseCapability, moduleCompletion )
抽象操作ContinueDynamicImport接受参数promiseCapability（一个import()
- 如果moduleCompletion是一个
突然完成 ，则- 执行!
Call (promiseCapability.[[Reject]],undefined , « moduleCompletion.[[Value]] »)。 - 返回
unused 。
- 执行!
- 设module为moduleCompletion.[[Value]]。
- 设loadPromise为 module.LoadRequestedModules()。
- 设rejectedClosure为一个新
抽象闭包 ，参数为(reason)，捕获promiseCapability，并执行以下步骤：- 执行!
Call (promiseCapability.[[Reject]],undefined , « reason »)。 - 返回
unused 。
- 执行!
- 设onRejected为
CreateBuiltinFunction (rejectedClosure, 1,"" , « »)。 - 设linkAndEvaluateClosure为一个新
抽象闭包 ，无参数，捕获module、promiseCapability和 onRejected，并执行以下步骤：- 设link为
Completion (module.Link())。 - 如果link是一个
突然完成 ，则- 执行!
Call (promiseCapability.[[Reject]],undefined , « link.[[Value]] »)。 - 返回
unused 。
- 执行!
- 设evaluatePromise为 module.Evaluate()。
- 设fulfilledClosure为一个新
抽象闭包 ，无参数，捕获module和promiseCapability，并执行以下步骤：- 设namespace为
GetModuleNamespace (module)。 - 执行!
Call (promiseCapability.[[Resolve]],undefined , « namespace »)。 - 返回
unused 。
- 设namespace为
- 设onFulfilled为
CreateBuiltinFunction (fulfilledClosure, 0,"" , « »)。 - 执行
PerformPromiseThen (evaluatePromise, onFulfilled, onRejected)。 - 返回
unused 。
- 设link为
- 设linkAndEvaluate为
CreateBuiltinFunction (linkAndEvaluateClosure, 0,"" , « »)。 - 执行
PerformPromiseThen (loadPromise, linkAndEvaluate, onRejected)。 - 返回
unused 。
13.3.11 标签模板
标签模板是一个函数调用，其中调用的参数是从一个
13.3.11.1 运行时语义：评估
- 设tagRef为?
Evaluation ofMemberExpression 。 - 设tagFunc为?
GetValue (tagRef)。 - 设thisCall为这个
MemberExpression 。 - 设tailCall为
IsInTailPosition (thisCall)。 - 返回?
EvaluateCall (tagFunc, tagRef,TemplateLiteral , tailCall)。
- 设tagRef为?
Evaluation ofCallExpression 。 - 设tagFunc为?
GetValue (tagRef)。 - 设thisCall为这个
CallExpression 。 - 设tailCall为
IsInTailPosition (thisCall)。 - 返回?
EvaluateCall (tagFunc, tagRef,TemplateLiteral , tailCall)。
13.3.12 元属性
13.3.12.1 运行时语义: Evaluation
- 返回
GetNewTarget ()。
- 设 module 为
GetActiveScriptOrModule ()。 断言 ：module 是一个源文本模块记录 。- 设 importMeta 为 module.[[ImportMeta]]。
- 如果 importMeta 是
empty ， 则- 设 importMeta 为
OrdinaryObjectCreate (null )。 - 设 importMetaValues 为
HostGetImportMetaProperties (module)。 - 对于每个
记录 { [[Key]], [[Value]] } p 的 importMetaValues，执行- 执行 !
CreateDataPropertyOrThrow (importMeta, p.[[Key]], p.[[Value]])。
- 执行 !
- 执行
HostFinalizeImportMeta (importMeta, module)。 - 设 module.[[ImportMeta]] 为 importMeta。
- 返回 importMeta。
- 设 importMeta 为
- 否则，
13.3.12.1.1 HostGetImportMetaProperties ( moduleRecord )
The import.meta 返回的对象。
HostGetImportMetaProperties 的默认实现是返回一个新的空
13.3.12.1.2 HostFinalizeImportMeta ( importMeta, moduleRecord )
The import.meta
返回的对象。
大多数
HostFinalizeImportMeta 的默认实现是返回
13.4 更新表达式
语法
13.4.1 静态语义：早期错误
-
如果
AssignmentTargetType 的LeftHandSideExpression 不是simple ，则是早期语法错误。
-
如果
AssignmentTargetType 的UnaryExpression 不是simple ，则是早期语法错误。
13.4.2 后置递增运算符
13.4.2.1 运行时语义：评估
- 设 lhs 为 ?
评估 的LeftHandSideExpression 。 - 设 oldValue 为 ?
ToNumeric (?GetValue (lhs))。 - 如果 oldValue
是一个 数字 ，则- 设 newValue 为
Number::add (oldValue,1 𝔽)。
- 设 newValue 为
- 否则，
断言 ：oldValue是一个 大整数 。- 设 newValue 为
BigInt::add (oldValue,1 ℤ)。
- 执行 ?
PutValue (lhs, newValue)。 - 返回 oldValue。
13.4.3 后置递减运算符
13.4.3.1 运行时语义：评估
- 设 lhs 为 ?
评估 的LeftHandSideExpression 。 - 设 oldValue 为 ?
ToNumeric (?GetValue (lhs))。 - 如果 oldValue
是一个 数字 ，则- 设 newValue 为
Number::subtract (oldValue,1 𝔽)。
- 设 newValue 为
- 否则，
断言 ：oldValue是一个 大整数 。- 设 newValue 为
BigInt::subtract (oldValue,1 ℤ)。
- 执行 ?
PutValue (lhs, newValue)。 - 返回 oldValue。
13.4.4 前置递增运算符
13.4.4.1 运行时语义：评估
- 设 expr 为 ?
评估 的UnaryExpression 。 - 设 oldValue 为 ?
ToNumeric (?GetValue (expr))。 - 如果 oldValue
是一个 数字 ，则- 设 newValue 为
Number::add (oldValue,1 𝔽)。
- 设 newValue 为
- 否则，
断言 ：oldValue是一个 大整数 。- 设 newValue 为
BigInt::add (oldValue,1 ℤ)。
- 执行 ?
PutValue (expr, newValue)。 - 返回 newValue。
13.4.5 前置递减运算符
13.4.5.1 运行时语义：评估
- 设 expr 为 ?
评估 的UnaryExpression 。 - 设 oldValue 为 ?
ToNumeric (?GetValue (expr))。 - 如果 oldValue
是一个 数字 ，则- 设 newValue 为
Number::subtract (oldValue,1 𝔽)。
- 设 newValue 为
- 否则，
断言 ：oldValue是一个 大整数 。- 设 newValue 为
BigInt::subtract (oldValue,1 ℤ)。
- 执行 ?
PutValue (expr, newValue)。 - 返回 newValue。
13.5 一元运算符
语法
13.5.1 The delete 运算符
13.5.1.1 静态语义：早期错误
-
如果
UnaryExpression 包含在严格模式代码 中，并且派生的UnaryExpression 是PrimaryExpression : IdentifierReference MemberExpression : MemberExpression . PrivateIdentifier CallExpression : CallExpression . PrivateIdentifier OptionalChain : ?. PrivateIdentifier OptionalChain : OptionalChain . PrivateIdentifier -
如果派生的
UnaryExpression 是
PrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
并且CoverParenthesizedExpressionAndArrowParameterList 最终派生出的短语，如果用于替代UnaryExpression ，将根据这些规则产生语法错误。此规则递归应用。
最后一项规则意味着表达式如 delete (((foo))) 会产生
13.5.1.2 运行时语义：评估
- 设 ref 为 ?
评估 的UnaryExpression 。 - 如果 ref 不是
引用记录 ，返回true 。 - 如果
IsUnresolvableReference (ref) 是true ，则断言 ：ref.[[Strict]] 是false 。- 返回
true 。
- 如果
IsPropertyReference (ref) 是true ，则断言 ：IsPrivateReference (ref) 是false 。- 如果
IsSuperReference (ref) 是true ，抛出ReferenceError 异常。 - 设 baseObj 为
?
ToObject (ref.[[Base]])。 - 设 deleteStatus 为 ? baseObj.[[Delete]](ref.[[ReferencedName]])。
- 如果 deleteStatus 是
false 并且 ref.[[Strict]] 是true ，抛出TypeError 异常。 - 返回 deleteStatus。
- 否则，
当 delete 运算符出现在 delete 运算符出现在
13.5.2 The void 运算符
13.5.2.1 运行时语义：评估
- 设 expr 为 ?
评估 的UnaryExpression 。 - 执行 ?
GetValue (expr)。 - 返回
undefined 。
13.5.3 The typeof 运算符
13.5.3.1 运行时语义：评估
- 设 val 为 ?
评估 的UnaryExpression 。 - 如果 val 是
引用记录 ，则- 如果
IsUnresolvableReference (val) 是true ，返回"undefined" 。
- 如果
- 设 val 为 ?
GetValue (val)。 - 如果 val 是
undefined ，返回"undefined" 。 - 如果 val 是
null ，返回"object" 。 - 如果 val
是字符串 ，返回"string" 。 - 如果 val
是符号 ，返回"symbol" 。 - 如果 val
是布尔值 ，返回"boolean" 。 - 如果 val
是数字 ，返回"number" 。 - 如果 val
是大整数 ，返回"bigint" 。 断言 ：val是对象 。- 注意：这一步在章节
B.3.6.3 中被替换。 - 如果 val 有 [[Call]]
内部槽，返回
"function" 。 - 返回
"object" 。
13.5.4 一元 + 运算符
一元 + 运算符将其操作数转换为
13.5.4.1 运行时语义：评估
- 设 expr 为 ?
评估 的UnaryExpression 。 - 返回 ?
ToNumber (?GetValue (expr))。
13.5.5 一元 - 运算符
一元 - 运算符将其操作数转换为数值，然后对其取反。取反
13.5.5.1 运行时语义：评估
- 设 expr 为 ?
评估 的UnaryExpression 。 - 设 oldValue 为 ?
ToNumeric (?GetValue (expr))。 - 如果 oldValue
是数字 ，则- 返回
Number::unaryMinus (oldValue)。
- 返回
- 否则，
断言 ：oldValue是大整数 。- 返回
BigInt::unaryMinus (oldValue)。
13.5.6 按位 NOT 运算符 ( ~ )
13.5.6.1 运行时语义：评估
- 设 expr 为 ?
评估 的UnaryExpression 。 - 设 oldValue 为 ?
ToNumeric (?GetValue (expr))。 - 如果 oldValue
是数字 ，则- 返回
Number::bitwiseNOT (oldValue)。
- 返回
- 否则，
断言 ：oldValue是大整数 。- 返回
BigInt::bitwiseNOT (oldValue)。
13.5.7 逻辑 NOT 运算符 ( ! )
13.5.7.1 运行时语义：评估
- 设 expr 为 ?
评估 的UnaryExpression 。 - 设 oldValue 为
ToBoolean (?GetValue (expr))。 - 如果 oldValue 是
true ，返回false 。 - 返回
true 。
13.6 幂运算符
语法
13.6.1 运行时语义：评估
13.7 乘法运算符
语法
- 运算符
*执行乘法，生成其操作数的乘积。 - 运算符
/执行除法，生成其操作数的商。 - 运算符
%生成其操作数在隐式除法中的余数。
13.7.1 运行时语义：评估
- 设 opText 为
源文本匹配的 MultiplicativeOperator 。 - 返回 ?
EvaluateStringOrNumericBinaryExpression (MultiplicativeExpression , opText,ExponentiationExpression )。
13.8 加法运算符
语法
13.8.1 加法运算符 ( + )
加法运算符既可以执行字符串连接，也可以执行数值加法。
13.8.1.1 运行时语义：评估
13.8.2 减法运算符 ( - )
减法运算符执行减法，生成其操作数的差值。
13.8.2.1 运行时语义：评估
13.9 位移运算符
语法
13.9.1 左移运算符 ( << )
对左操作数执行按位左移操作，移动的位数由右操作数指定。
13.9.1.1 运行时语义：评估
13.9.2 带符号右移运算符 ( >> )
对左操作数执行按位右移操作，移动的位数由右操作数指定，并使用符号位填充空出的位。
13.9.2.1 运行时语义：评估
13.9.3 无符号右移运算符 ( >>> )
对左操作数执行按位右移操作，移动的位数由右操作数指定，并使用零填充空出的位。
13.9.3.1 运行时语义：评估
13.10 关系运算符
关系运算符的求值结果总是布尔类型，反映运算符命名的关系是否在其两个操作数之间成立。
语法
[In] 语法参数是为了避免在关系表达式中混淆 in 运算符和 for 语句中的 in 运算符。
13.10.1 运行时语义: 求值
-
让 lref 为 ?
Evaluation ofRelationalExpression 。 -
让 lval 为 ?
GetValue (lref)。 -
让 rref 为 ?
Evaluation ofShiftExpression 。 -
让 rval 为 ?
GetValue (rref)。 -
让 r 为 ?
IsLessThan (lval, rval,true )。 -
如果 r 是
undefined ，返回false 。否则，返回 r。
-
让 lref 为 ?
Evaluation ofRelationalExpression 。 -
让 lval 为 ?
GetValue (lref)。 -
让 rref 为 ?
Evaluation ofShiftExpression 。 -
让 rval 为 ?
GetValue (rref)。 -
让 r 为 ?
IsLessThan (rval, lval,false )。 -
如果 r 是
undefined ，返回false 。否则，返回 r。
-
让 lref 为 ?
Evaluation ofRelationalExpression 。 -
让 lval 为 ?
GetValue (lref)。 -
让 rref 为 ?
Evaluation ofShiftExpression 。 -
让 rval 为 ?
GetValue (rref)。 -
让 r 为 ?
IsLessThan (rval, lval,false )。 -
如果 r 是
true 或undefined ，返回false 。否则，返回true 。
-
让 lref 为 ?
Evaluation ofRelationalExpression 。 -
让 lval 为 ?
GetValue (lref)。 -
让 rref 为 ?
Evaluation ofShiftExpression 。 -
让 rval 为 ?
GetValue (rref)。 -
让 r 为 ?
IsLessThan (lval, rval,true )。 -
如果 r 是
true 或undefined ，返回false 。否则，返回true 。
-
让 lref 为 ?
Evaluation ofRelationalExpression 。 -
让 lval 为 ?
GetValue (lref)。 -
让 rref 为 ?
Evaluation ofShiftExpression 。 -
让 rval 为 ?
GetValue (rref)。 -
返回 ?
InstanceofOperator (lval, rval)。
-
让 lref 为 ?
Evaluation ofRelationalExpression 。 -
让 lval 为 ?
GetValue (lref)。 -
让 rref 为 ?
Evaluation ofShiftExpression 。 -
让 rval 为 ?
GetValue (rref)。 -
如果 rval
不是对象 ，抛出TypeError 异常。 -
返回 ?
HasProperty (rval，?ToPropertyKey (lval))。
-
让 privateIdentifier 为
StringValue ofPrivateIdentifier 。 -
让 rref 为 ?
Evaluation ofShiftExpression 。 -
让 rval 为 ?
GetValue (rref)。 -
如果 rval
不是对象 ，抛出TypeError 异常。 -
让 privateEnv 为
运行执行上下文 的 PrivateEnvironment。 -
让 privateName 为
ResolvePrivateIdentifier (privateEnv，privateIdentifier)。 -
如果
PrivateElementFind (rval，privateName) 不是empty ，返回true 。 -
返回
false 。
13.10.2 InstanceofOperator ( V, target )
抽象操作 InstanceofOperator 接受参数 V（一个
-
如果 target
不是对象 ，抛出TypeError 异常。 -
让 instOfHandler 为 ?
GetMethod (target，@@hasInstance )。 -
如果 instOfHandler 不是
undefined ，则 -
如果
IsCallable (target) 是false ，抛出TypeError 异常。 -
返回 ?
OrdinaryHasInstance (target，V)。
步骤
instanceof 运算符语义。如果对象没有定义或继承
instanceof 语义。
13.11 等值运算符
等值运算符的求值结果总是布尔类型，反映运算符命名的关系是否在其两个操作数之间成立。
语法
13.11.1 运行时语义：求值
-
让 lref 为 ?
Evaluation ofEqualityExpression 。 -
让 lval 为 ?
GetValue (lref)。 -
让 rref 为 ?
Evaluation ofRelationalExpression 。 -
让 rval 为 ?
GetValue (rref)。 -
返回 ?
IsLooselyEqual (rval, lval)。
-
让 lref 为 ?
Evaluation ofEqualityExpression 。 -
让 lval 为 ?
GetValue (lref)。 -
让 rref 为 ?
Evaluation ofRelationalExpression 。 -
让 rval 为 ?
GetValue (rref)。 -
让 r 为 ?
IsLooselyEqual (rval, lval)。 -
如果 r 是
true ，返回false 。否则，返回true 。
-
让 lref 为 ?
Evaluation ofEqualityExpression 。 -
让 lval 为 ?
GetValue (lref)。 -
让 rref 为 ?
Evaluation ofRelationalExpression 。 -
让 rval 为 ?
GetValue (rref)。 -
返回
IsStrictlyEqual (rval, lval)。
-
让 lref 为 ?
Evaluation ofEqualityExpression 。 -
让 lval 为 ?
GetValue (lref)。 -
让 rref 为 ?
Evaluation ofRelationalExpression 。 -
让 rval 为 ?
GetValue (rref)。 -
让 r 为
IsStrictlyEqual (rval, lval)。 -
如果 r 是
true ，返回false 。否则，返回true 。
根据上述等值定义：
-
字符串比较可以通过：
`${a}` == `${b}`强制进行。 -
数字比较可以通过：
+a == +b强制进行。 -
布尔值比较可以通过：
!a == !b强制进行。
等值运算符保持以下不变量：
-
A != B等价于!(A == B)。 -
A == B等价于B == A，除了A和B的求值顺序。
等值运算符并不总是传递的。例如，可能存在两个不同的字符串对象，每个对象表示相同的字符串值；每个字符串对象会被 == 运算符视为与字符串值相等，但这两个字符串对象彼此并不相等。例如：
-
new String("a") == "a"和"a" == new String("a")均为true 。 -
new String("a") == new String("a")为false 。
字符串比较使用简单的代码单元值相等测试。不会尝试使用 Unicode 规范中定义的更复杂的、语义导向的字符或字符串相等性定义和排序顺序。因此，根据 Unicode 标准规范等价的字符串值可能会被测试为不相等。实际上，这个算法假设两个字符串都已处于规范化形式。
13.12 二进制按位运算符
语法
13.12.1 运行时语义：求值
13.13 二进制逻辑运算符
语法
由 && 或 || 运算符生成的值不一定是布尔类型。生成的值始终是两个操作数表达式之一的值。
13.13.1 运行时语义：求值
-
令 lref 为 ?
Evaluation ofLogicalANDExpression 。 -
令 lval 为 ?
GetValue (lref)。 -
令 lbool 为
ToBoolean (lval)。 -
如果 lbool 为
false ，则返回 lval。 -
令 rref 为 ?
Evaluation ofBitwiseORExpression 。 -
返回 ?
GetValue (rref)。
-
令 lref 为 ?
Evaluation ofLogicalORExpression 。 -
令 lval 为 ?
GetValue (lref)。 -
令 lbool 为
ToBoolean (lval)。 -
如果 lbool 为
true ，则返回 lval。 -
令 rref 为 ?
Evaluation ofLogicalANDExpression 。 -
返回 ?
GetValue (rref)。
-
令 lref 为 ?
Evaluation ofCoalesceExpressionHead 。 -
令 lval 为 ?
GetValue (lref)。 -
如果 lval 是
undefined 或null ，则-
令 rref 为 ?
Evaluation ofBitwiseORExpression 。 -
返回 ?
GetValue (rref)。
-
令 rref 为 ?
-
否则，
- 返回 lval。
13.14 条件操作符（? :）
语法
ECMAScript 中
13.14.1 运行时语义：求值
-
令 lref 为 ?
Evaluation ofShortCircuitExpression 。 -
令 lval 为
ToBoolean (?GetValue (lref))。 -
如果 lval 为
true ，则-
令 trueRef 为 ?
Evaluation of 第一个AssignmentExpression 。 -
返回 ?
GetValue (trueRef)。
-
令 trueRef 为 ?
-
否则，
-
令 falseRef 为 ?
Evaluation of 第二个AssignmentExpression 。 -
返回 ?
GetValue (falseRef)。
-
令 falseRef 为 ?
13.15 赋值操作符
语法
13.15.1 静态语义：早期错误
如果
如果
-
如果
AssignmentTargetType 的LeftHandSideExpression 不是simple ，则为语法错误。
-
如果
AssignmentTargetType 的LeftHandSideExpression 不是simple ，则为语法错误。
13.15.2 运行时语义：求值
-
如果
LeftHandSideExpression 既不是ObjectLiteral 也不是ArrayLiteral ，则：-
让
lref是对
Evaluation 的LeftHandSideExpression 的求值。 -
如果
IsAnonymousFunctionDefinition (AssignmentExpression )和IsIdentifierRef 的LeftHandSideExpression 都为true ，则：-
让
rval是对
NamedEvaluation (AssignmentExpression )，带有参数lref.[[ReferencedName]]。
-
让
rval是对
-
否则，
-
让
rref是对
Evaluation (AssignmentExpression )的求值。 -
让
rval是对
GetValue (rref)的求值。
-
让
rref是对
-
执行
PutValue ( lref，rval)。 - 返回rval。
-
让
lref是对
-
让
assignmentPattern成为
AssignmentPattern ，由涵盖 的LeftHandSideExpression 。 -
让
rref是对
Evaluation (AssignmentExpression )的求值。 -
让
rval是对
GetValue (rref)的求值。 -
执行
DestructuringAssignmentEvaluation 的assignmentPattern，带有参数rval。 - 返回rval。
-
让
lref是对
Evaluation 的LeftHandSideExpression 的求值。 -
让
lval是对
GetValue (lref)的求值。 -
让
rref是对
Evaluation 的AssignmentExpression 的求值。 -
让
rval是对
GetValue (rref)的求值。 -
让
assignmentOpText是
源文本匹配 的AssignmentOperator 。 -
让
opText成为以下表格中与assignmentOpText关联的Unicode代码点序列：
assignmentOpText opText **=***=*/=/%=%+=+-=-<<=<<>>=>>>>>=>>>&=&^=^|=| -
让
r是对
ApplyStringOrNumericBinaryOperator ( lval， opText， rval)的求值。 -
执行
PutValue ( lref， r)。 - 返回r。
-
让
lref是对
Evaluation 的LeftHandSideExpression 的求值。 -
让
lval是对
GetValue (lref)的求值。 -
让
lbool是
ToBoolean (lval)的求值。 -
如果lbool为
false ，返回lval。 -
如果
IsAnonymousFunctionDefinition (AssignmentExpression )为true ，且IsIdentifierRef 的LeftHandSideExpression 为true ，则：-
让
rval是对
NamedEvaluation (AssignmentExpression )，带有参数 lref.[[ReferencedName]]。
-
让
rval是对
-
否则，
-
让
rref是对
Evaluation 的AssignmentExpression 的求值。 -
让
rval是对
GetValue (rref)的求值。
-
让
rref是对
-
执行
PutValue ( lref，rval)。 - 返回rval。
-
让
lref是对
Evaluation 的LeftHandSideExpression 的求值。 -
让
lval是对
GetValue (lref)的求值。 -
让
lbool是
ToBoolean (lval)的求值。 -
如果lbool为
true ，返回lval。 -
如果
IsAnonymousFunctionDefinition (AssignmentExpression )为true ，且IsIdentifierRef 的LeftHandSideExpression 为true ，则：-
让
rval是对
NamedEvaluation (AssignmentExpression )，带有参数 lref.[[ReferencedName]]。
-
让
rval是对
-
否则，
-
让
rref是对
Evaluation 的AssignmentExpression 的求值。 -
让
rval是对
GetValue (rref)的求值。
-
让
rref是对
-
执行
PutValue ( lref，rval)。 - 返回rval。
-
让
lref是对
Evaluation 的LeftHandSideExpression 的求值。 -
让
lval是对
GetValue (lref)的求值。 -
如果
lval既不是
undefined 也不是null ，返回 lval。 -
如果
IsAnonymousFunctionDefinition (AssignmentExpression )为true ，且IsIdentifierRef 的LeftHandSideExpression 为true ，则：-
让
rval是对
NamedEvaluation (AssignmentExpression )，带有参数 lref.[[ReferencedName]]。
-
让
rval是对
-
否则，
-
让
rref是对
Evaluation 的AssignmentExpression 的求值。 -
让
rval是对
GetValue (rref)的求值。
-
让
rref是对
-
执行
PutValue ( lref，rval)。 - 返回rval。
13.15.3 ApplyStringOrNumericBinaryOperator ( lval, opText, rval )
抽象操作 ApplyStringOrNumericBinaryOperator 接受参数 lval（一个 **、*、/、%、+、-、<<、>>、>>>、&、^
或 |）和 rval（一个
-
如果 opText 是
+，则-
令 lprim 为 ?
ToPrimitive (lval)。 -
令 rprim 为 ?
ToPrimitive (rval)。 -
如果 lprim 是
字符串 或 rprim 是字符串 ，则 - 将 lval 设置为 lprim。
- 将 rval 设置为 rprim。
-
令 lprim 为 ?
- 注意：此时，它必须是一个数值运算。
-
令 lnum 为 ?
ToNumeric (lval)。 -
令 rnum 为 ?
ToNumeric (rval)。 -
如果 lnum 的
类型 与 rnum 的类型 不同，抛出一个TypeError 异常。 -
如果 lnum 是
BigInt ，则-
如果 opText 是
**，返回 ?BigInt::exponentiate (lnum, rnum)。 -
如果 opText 是
/，返回 ?BigInt::divide (lnum, rnum)。 -
如果 opText 是
%，返回 ?BigInt::remainder (lnum, rnum)。 -
如果 opText 是
>>>，返回 ?BigInt::unsignedRightShift (lnum, rnum)。
-
如果 opText 是
-
令 operation 为与以下表格中的 opText 和 lnum 的
类型 相关的抽象操作：opText 类型 (lnum)operation **Number Number::exponentiate *Number Number::multiply *BigInt BigInt::multiply /Number Number::divide %Number Number::remainder +Number Number::add +BigInt BigInt::add -Number Number::subtract -BigInt BigInt::subtract <<Number Number::leftShift <<BigInt BigInt::leftShift >>Number Number::signedRightShift >>BigInt BigInt::signedRightShift >>>Number Number::unsignedRightShift &Number Number::bitwiseAND &BigInt BigInt::bitwiseAND ^Number Number::bitwiseXOR ^BigInt BigInt::bitwiseXOR |Number Number::bitwiseOR |BigInt BigInt::bitwiseOR - 返回 operation(lnum, rnum)。
在步骤
步骤
13.15.4 EvaluateStringOrNumericBinaryExpression ( leftOperand, opText, rightOperand )
抽象操作 EvaluateStringOrNumericBinaryExpression 接受参数 leftOperand（一个
- 让 lref 为 ?
Evaluation 的 leftOperand。 - 让 lval 为 ?
GetValue (lref)。 - 让 rref 为 ?
Evaluation 的 rightOperand。 - 让 rval 为 ?
GetValue (rref)。 - 返回 ?
ApplyStringOrNumericBinaryOperator (lval, opText, rval)。
13.15.5 解构赋值
补充语法
在处理以下产生式的实例时
对于
13.15.5.1 静态语义：早期错误
-
如果
AssignmentTargetType 的IdentifierReference 不是simple ，则这是一个语法错误。
-
如果
DestructuringAssignmentTarget 是ArrayLiteral 或ObjectLiteral ，则这是一个语法错误。
如果
如果
-
如果
AssignmentTargetType 的LeftHandSideExpression 不是simple ，则这是一个语法错误。
13.15.5.2 运行时语义：DestructuringAssignmentEvaluation
- 执行 ?
RequireObjectCoercible (value)。 - 返回
unused 。
- 执行 ?
RequireObjectCoercible (value)。 - 执行 ?
PropertyDestructuringAssignmentEvaluation ofAssignmentPropertyList with argument value。 - 返回
unused 。
- 执行 ?
RequireObjectCoercible (value)。 - 让 excludedNames 成为一个新的空的
列表 。 - 返回 ?
RestDestructuringAssignmentEvaluation ofAssignmentRestProperty with arguments value 和 excludedNames。
- 执行 ?
RequireObjectCoercible (value)。 - 让 excludedNames 成为 ?
PropertyDestructuringAssignmentEvaluation ofAssignmentPropertyList with argument value。 - 返回 ?
RestDestructuringAssignmentEvaluation ofAssignmentRestProperty with arguments value 和 excludedNames。
- 让 iteratorRecord 成为 ?
GetIterator (value,sync )。 - 返回 ?
IteratorClose (iteratorRecord,NormalCompletion (unused ))。
- 让 iteratorRecord 成为 ?
GetIterator (value,sync )。 - 让 result 成为
Completion (IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord)。 - 如果 iteratorRecord.[[Done]] 为
false ，返回 ?IteratorClose (iteratorRecord, result)。 - 返回 result。
- 让 iteratorRecord 成为 ?
GetIterator (value,sync )。 - 如果
Elision 存在，则- 让 status 成为
Completion (IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord)。 - 如果 status 是一个
突然完成 ，则断言 : iteratorRecord.[[Done]] 为true 。- 返回 ? status。
- 让 status 成为
- 让 result 成为
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentRestElement with argument iteratorRecord)。 - 如果 iteratorRecord.[[Done]] 为
false ，返回 ?IteratorClose (iteratorRecord, result)。 - 返回 result。
- 让 iteratorRecord 成为 ?
GetIterator (value,sync )。 - 让 status 成为
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentElementList with argument iteratorRecord)。 - 如果 status 是一个
突然完成 ，则- 如果 iteratorRecord.[[Done]] 为
false ，返回 ?IteratorClose (iteratorRecord, status)。 - 返回 ? status。
- 如果 iteratorRecord.[[Done]] 为
- 如果
Elision 存在，则- 设置 status 为
Completion (IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord)。 - 如果 status 是一个
突然完成 ，则断言 : iteratorRecord.[[Done]] 为true 。- 返回 ? status。
- 设置 status 为
- 如果
AssignmentRestElement 存在，则- 设置 status 为
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentRestElement with argument iteratorRecord)。
- 设置 status 为
- 如果 iteratorRecord.[[Done]] 为
false ，返回 ?IteratorClose (iteratorRecord, status)。 - 返回 ? status。
13.15.5.3 运行时语义：属性解构赋值求值
语法指导操作
- 让 propertyNames 是 ?
PropertyDestructuringAssignmentEvaluation 对AssignmentPropertyList 调用时的参数 value。 - 让 nextNames 是 ?
PropertyDestructuringAssignmentEvaluation 对AssignmentProperty 调用时的参数 value。 - 返回 propertyNames 和 nextNames 的
列表连接 。
- 让 P 是
StringValue 的IdentifierReference 。 - 让 lref 是 ?
ResolveBinding (P)。 - 让 v 是 ?
GetV (value, P)。 - 如果
Initializer 存在并且 v 是undefined ，则- 如果
IsAnonymousFunctionDefinition (Initializer ) 为true ，则- 将 v 设置为 ?
NamedEvaluation 的Initializer 参数为 P。
- 将 v 设置为 ?
- 否则,
- 让 defaultValue 是 ?
Evaluation 的Initializer 。 - 将 v 设置为 ?
GetValue (defaultValue)。
- 让 defaultValue 是 ?
- 如果
- 执行 ?
PutValue (lref, v)。 - 返回 « P »。
- 让 name 是 ?
Evaluation 的PropertyName 。 - 执行 ?
KeyedDestructuringAssignmentEvaluation 的AssignmentElement 参数为 value 和 name。 - 返回 « name »。
13.15.5.4 运行时语义：RestDestructuringAssignmentEvaluation
语法指导操作
- 让 lref 是 ?
Evaluation 的DestructuringAssignmentTarget 。 - 让 restObj 是
OrdinaryObjectCreate (%Object.prototype% )。 - 执行 ?
CopyDataProperties (restObj, value, excludedNames)。 - 返回 ?
PutValue (lref, restObj)。
13.15.5.5 运行时语义：IteratorDestructuringAssignmentEvaluation
语法指导操作
- 返回 ?
IteratorDestructuringAssignmentEvaluation 的AssignmentElisionElement 传入参数 iteratorRecord。
- 执行 ?
IteratorDestructuringAssignmentEvaluation 的AssignmentElementList 传入参数 iteratorRecord。 - 返回 ?
IteratorDestructuringAssignmentEvaluation 的AssignmentElisionElement 传入参数 iteratorRecord。
- 返回 ?
IteratorDestructuringAssignmentEvaluation 的AssignmentElement 传入参数 iteratorRecord。
- 执行 ?
IteratorDestructuringAssignmentEvaluation 的Elision 传入参数 iteratorRecord。 - 返回 ?
IteratorDestructuringAssignmentEvaluation 的AssignmentElement 传入参数 iteratorRecord。
- 如果 iteratorRecord.[[Done]]
是
false ，那么- 令 next 为
Completion (IteratorStep (iteratorRecord))。 - 如果 next 是一个
异常完成 ，设置 iteratorRecord.[[Done]] 为true 。 ReturnIfAbrupt (next)。- 如果 next 是
false ，设置 iteratorRecord.[[Done]] 为true 。
- 令 next 为
- 返回
unused 。
- 执行 ?
IteratorDestructuringAssignmentEvaluation 的Elision 传入参数 iteratorRecord。 - 如果 iteratorRecord.[[Done]]
是
false ，那么- 令 next 为
Completion (IteratorStep (iteratorRecord))。 - 如果 next 是一个
异常完成 ，设置 iteratorRecord.[[Done]] 为true 。 ReturnIfAbrupt (next)。- 如果 next 是
false ，设置 iteratorRecord.[[Done]] 为true 。
- 令 next 为
- 返回
unused 。
- 如果
DestructuringAssignmentTarget 既不是一个ObjectLiteral 也不是一个ArrayLiteral ，那么- 令 lref 为 ?
Evaluation 的DestructuringAssignmentTarget 。
- 令 lref 为 ?
- 令 value 为
undefined 。 - 如果 iteratorRecord.[[Done]]
是
false ，那么- 令 next 为 ?
IteratorStepValue 的 iteratorRecord。 - 如果 next 不是
done ，那么- 设置 value 为 next。
- 令 next 为 ?
- 如果
Initializer 存在并且 value 是undefined ，那么- 如果
IsAnonymousFunctionDefinition (Initializer ) 是true 并且IsIdentifierRef 的DestructuringAssignmentTarget 是true ，那么- 令 v 为 ?
NamedEvaluation 的Initializer 传入参数 lref.[[ReferencedName]]。
- 令 v 为 ?
- 否则，
- 令 defaultValue 为 ?
Evaluation 的Initializer 。 - 令 v 为 ?
GetValue (defaultValue)。
- 令 defaultValue 为 ?
- 如果
- 否则，
- 令 v 为 value。
- 如果
DestructuringAssignmentTarget 是一个ObjectLiteral 或一个ArrayLiteral ，那么- 令 nestedAssignmentPattern 为一个
AssignmentPattern ， 它被覆盖 在DestructuringAssignmentTarget 。 - 返回 ?
DestructuringAssignmentEvaluation 的 nestedAssignmentPattern 传入参数 v。
- 令 nestedAssignmentPattern 为一个
- 返回 ?
PutValue (lref, v)。
从左到右的求值顺序通过在访问迭代器或求值
- 如果
DestructuringAssignmentTarget 既不是一个ObjectLiteral 也不是一个ArrayLiteral ，那么- 令 lref 为 ?
Evaluation 的DestructuringAssignmentTarget 。
- 令 lref 为 ?
- 令 A 为 !
ArrayCreate (0)。 - 令 n 为 0。
- 重复，直到 iteratorRecord.[[Done]]
是
false ，- 令 next 为 ?
IteratorStepValue 的 iteratorRecord。 - 如果 next 不是
done ，那么- 执行 !
CreateDataPropertyOrThrow 的 A， !ToString 的𝔽 的 n， next。 - 设置 n 为 n + 1。
- 执行 !
- 令 next 为 ?
- 如果
DestructuringAssignmentTarget 既不是一个ObjectLiteral 也不是一个ArrayLiteral ，那么- 返回 ?
PutValue 的 lref，A。
- 返回 ?
- 令 nestedAssignmentPattern 为一个
AssignmentPattern ， 它被覆盖 在DestructuringAssignmentTarget 。 - 返回 ?
DestructuringAssignmentEvaluation 的 nestedAssignmentPattern 传入参数 A。
13.15.5.6 运行时语义：KeyedDestructuringAssignmentEvaluation
-
如果
DestructuringAssignmentTarget 既不是ObjectLiteral 也不是ArrayLiteral ，那么-
令 lref 为 ?
Evaluation 的DestructuringAssignmentTarget 。
-
令 lref 为 ?
-
令 v 为 ?
GetV 的 value 和 propertyName。 -
如果
Initializer 存在并且 v 是undefined ，那么-
如果
IsAnonymousFunctionDefinition 的Initializer 并且IsIdentifierRef 的DestructuringAssignmentTarget 都为true ，那么-
令 rhsValue 为 ?
NamedEvaluation 的Initializer 传入参数 lref.[[ReferencedName]]。
-
令 rhsValue 为 ?
-
否则，
-
令 defaultValue 为 ?
Evaluation 的Initializer 。 -
令 rhsValue 为 ?
GetValue 的 defaultValue。
-
令 defaultValue 为 ?
-
如果
-
否则，
- 令 rhsValue 为 v。
-
如果
DestructuringAssignmentTarget 是一个ObjectLiteral 或ArrayLiteral ，那么-
令 assignmentPattern 为
AssignmentPattern ，它被覆盖 在DestructuringAssignmentTarget 。 -
返回 ?
DestructuringAssignmentEvaluation 的 assignmentPattern 传入参数 rhsValue。
-
令 assignmentPattern 为
-
返回 ?
PutValue 的 lref，rhsValue。
13.16 逗号操作符 (,)
语法
13.16.1 运行时语义：Evaluation
-
令 lref 为 ?
Evaluation 的Expression 。 -
执行 ?
GetValue (lref)。 -
令 rref 为 ?
Evaluation 的AssignmentExpression 。 -
返回 ?
GetValue (rref)。
14 ECMAScript 语言：语句和声明
语法
14.1 语句语义
14.1.1 运行时语义：求值
- 返回
empty 。
- 返回 ?
求值 ofFunctionDeclaration 。
- 令 newLabelSet 为一个空的
List 。 - 返回 ?
LabelledEvaluation of thisBreakableStatement with argument newLabelSet。
14.2 块
语法
14.2.1 静态语义：早期错误
-
如果
LexicallyDeclaredNames ofStatementList 包含任何重复条目，则为语法错误。 -
如果
LexicallyDeclaredNames ofStatementList 中的任何元素也出现在VarDeclaredNames ofStatementList 中，则为语法错误。
14.2.2 运行时语义：求值
- 返回
empty 。
- 令 oldEnv 为
运行中的执行上下文 的 LexicalEnvironment。 - 令 blockEnv 为
NewDeclarativeEnvironment (oldEnv)。 - 执行
BlockDeclarationInstantiation (StatementList , blockEnv)。 - 将
运行中的执行上下文 的 LexicalEnvironment 设置为 blockEnv。 - 令 blockValue 为
Completion (求值 ofStatementList )。 - 将
运行中的执行上下文 的 LexicalEnvironment 设置为 oldEnv。 - 返回 ? blockValue。
无论控制如何离开
- 令 sl 为 ?
求值 ofStatementList 。 - 令 s 为
Completion (求值 ofStatementListItem )。 - 返回 ?
UpdateEmpty (s, sl)。
eval 函数的调用都返回值 1：
eval("1;;;;;")
eval("1;{}")
eval("1;var a;")14.2.3 BlockDeclarationInstantiation ( code, env )
抽象操作 BlockDeclarationInstantiation 接受参数 code（一个
当调用时，它执行以下步骤：
- 令 declarations 为 code 的
LexicallyScopedDeclarations 。 - 令 privateEnv 为
运行中的执行上下文 的 PrivateEnvironment。 - 对于 declarations 的每个元素 d，执行
- 对于 d 的
BoundNames 的每个元素 dn，执行- 如果 d 的
IsConstantDeclaration 为true ，则- 执行
! env.CreateImmutableBinding(dn,
true )。
- 执行
! env.CreateImmutableBinding(dn,
- 否则，
- 执行 ! env.CreateMutableBinding(dn,
false )。注意：此步骤在B.3.2.6 中被替换。
- 执行 ! env.CreateMutableBinding(dn,
- 如果 d 的
- 如果 d 是
FunctionDeclaration 、GeneratorDeclaration 、AsyncFunctionDeclaration 或AsyncGeneratorDeclaration ，则- 令 fn 为 d 的
BoundNames 的唯一元素。 - 令 fo 为 d 的
InstantiateFunctionObject ，参数为 env 和 privateEnv。 - 执行 ! env.InitializeBinding(fn, fo)。注意：此步骤在
B.3.2.6 中被替换。
- 令 fn 为 d 的
- 对于 d 的
- 返回
unused 。
14.3 声明和变量语句
14.3.1 Let 和 Const 声明
let 和 const 声明定义的变量作用域为 let 声明中的
语法
14.3.1.1 静态语义：早期错误
-
如果
BoundNames ofBindingList 包含"let" ，则为语法错误。 -
如果
BoundNames ofBindingList 包含任何 重复条目，则为语法错误。
-
如果
Initializer 不存在且IsConstantDeclaration of theLexicalDeclaration 包含此LexicalBinding 为true ，则为语法错误。
14.3.1.2 运行时语义：求值
- 执行 ?
求值 ofBindingList 。 - 返回
empty 。
- 执行 ?
求值 ofBindingList 。 - 返回 ?
求值 ofLexicalBinding 。
- 令 lhs 为 !
ResolveBinding (StringValue ofBindingIdentifier )。 - 执行 !
InitializeReferencedBinding (lhs,undefined )。 - 返回
empty 。
一个 const 声明中。
- 令 bindingId 为
StringValue ofBindingIdentifier 。 - 令 lhs 为 !
ResolveBinding (bindingId)。 - 如果
IsAnonymousFunctionDefinition (Initializer ) istrue ，则- 令 value 为 ?
NamedEvaluation ofInitializer with argument bindingId。
- 令 value 为 ?
- 否则，
- 令 rhs 为 ?
求值 ofInitializer 。 - 令 value 为 ?
GetValue (rhs)。
- 令 rhs 为 ?
- 执行 !
InitializeReferencedBinding (lhs, value)。 - 返回
empty 。
- 令 rhs 为 ?
求值 ofInitializer 。 - 令 value 为 ?
GetValue (rhs)。 - 令 env 为
运行中的执行上下文 的 LexicalEnvironment。 - 返回 ?
BindingInitialization ofBindingPattern with arguments value and env。
14.3.2 变量语句
一个 var 语句声明的变量作用域为
语法
14.3.2.1 运行时语义：求值
- 执行 ?
求值 ofVariableDeclarationList 。 - 返回
empty 。
- 执行 ?
求值 ofVariableDeclarationList 。 - 返回 ?
求值 ofVariableDeclaration 。
- 返回
empty 。
- 令 bindingId 为
StringValue ofBindingIdentifier 。 - 令 lhs 为 ?
ResolveBinding (bindingId)。 - 如果
IsAnonymousFunctionDefinition (Initializer ) istrue ，则- 令 value 为 ?
NamedEvaluation ofInitializer with argument bindingId。
- 令 value 为 ?
- 否则，
- 令 rhs 为 ?
求值 ofInitializer 。 - 令 value 为 ?
GetValue (rhs)。
- 令 rhs 为 ?
- 执行 ?
PutValue (lhs, value)。 - 返回
empty 。
如果一个
- 令 rhs 为 ?
求值 ofInitializer 。 - 令 rval 为 ?
GetValue (rhs)。 - 返回 ?
BindingInitialization ofBindingPattern with arguments rval andundefined 。
14.3.3 解构绑定模式
语法
14.3.3.1 运行时语义：属性绑定初始化
属性绑定初始化是一个
- 令 boundNames 为 ?
属性绑定初始化 ofBindingPropertyList 使用参数 value 和 environment。 - 令 nextNames 为 ?
属性绑定初始化 ofBindingProperty 使用参数 value 和 environment。 - 返回 boundNames 和 nextNames 的
列表连接 。
- 令 name 为
SingleNameBinding 的BoundNames 的唯一元素。 - 执行 ?
键绑定初始化 ofSingleNameBinding 使用参数 value、environment 和 name。 - 返回 « name »。
- 令 P 为 ?
求值 ofPropertyName 。 - 执行 ?
键绑定初始化 ofBindingElement 使用参数 value、environment 和 P。 - 返回 « P »。
14.3.3.2 运行时语义：剩余绑定初始化
剩余绑定初始化是一个
- 令 lhs 为 ?
ResolveBinding (StringValue ofBindingIdentifier , environment)。 - 令 restObj 为
OrdinaryObjectCreate (%Object.prototype% )。 - 执行 ?
CopyDataProperties (restObj, value, excludedNames)。 - 如果 environment 是
undefined ， 返回 ?PutValue (lhs, restObj)。 - 返回 ?
InitializeReferencedBinding (lhs, restObj)。
14.3.3.3 运行时语义：键绑定初始化
键绑定初始化是一个
它在以下产生式上分段定义：
- 令 v 为 ?
GetV (value, propertyName)。 - 如果
Initializer 存在且 v 是undefined ，则- 令 defaultValue 为 ?
求值 ofInitializer 。 - 设置 v 为 ?
GetValue (defaultValue)。
- 令 defaultValue 为 ?
- 返回 ?
绑定初始化 ofBindingPattern 使用参数 v 和 environment。
- 令 bindingId 为
StringValue ofBindingIdentifier 。 - 令 lhs 为 ?
ResolveBinding (bindingId, environment)。 - 令 v 为 ?
GetV (value, propertyName)。 - 如果
Initializer 存在且 v 是undefined ，则- 如果
IsAnonymousFunctionDefinition (Initializer ) istrue ，则- 设置 v 为 ?
NamedEvaluation ofInitializer with argument bindingId。
- 设置 v 为 ?
- 否则，
- 令 defaultValue 为 ?
求值 ofInitializer 。 - 设置 v 为 ?
GetValue (defaultValue)。
- 令 defaultValue 为 ?
- 如果
- 如果 environment 是
undefined ， 返回 ?PutValue (lhs, v)。 - 返回 ?
InitializeReferencedBinding (lhs, v)。
14.4 空语句
语法
14.4.1 运行时语义：求值
- 返回
empty 。
14.5 表达式语句
语法
一个 function 或 class async function 开始，因为这可能会使其与一个 let [ 开始，因为这可能会使其与一个 let
14.5.1 运行时语义：求值
- 令 exprRef 为 ?
求值 ofExpression 。 - 返回 ?
GetValue (exprRef)。
14.6 if 语句
语法
else] 以通常的方式解决了经典的“悬空 else”问题。也就是说，当关联的
if 选择不明确时，else 与最近的（最内层的）候选 if 相关联。
14.6.1 静态语义：早期错误
-
如果
IsLabelledFunction (第一个Statement ) 是true ，则为语法错误。 -
如果
IsLabelledFunction (第二个Statement ) 是true ，则为语法错误。
-
如果
IsLabelledFunction (Statement ) 是true ，则为语法错误。
只有在实现
14.6.2 运行时语义：求值
- 设 exprRef 为 ?
求值 ofExpression . - 设 exprValue 为
ToBoolean (?GetValue (exprRef)). - 如果 exprValue 是
true ，则- 设 stmtCompletion 为
Completion (求值 of the firstStatement ).
- 设 stmtCompletion 为
- 否则
- 设 stmtCompletion 为
Completion (求值 of the secondStatement ).
- 设 stmtCompletion 为
- 返回 ?
UpdateEmpty (stmtCompletion,undefined ).
- 设 exprRef 为 ?
求值 ofExpression . - 设 exprValue 为
ToBoolean (?GetValue (exprRef)). - 如果 exprValue 是
false ，则- 返回
undefined .
- 返回
- 否则
- 设 stmtCompletion 为
Completion (求值 ofStatement ). - 返回 ?
UpdateEmpty (stmtCompletion,undefined ).
- 设 stmtCompletion 为
14.7 迭代语句
语法
14.7.1 语义
14.7.1.1 LoopContinues ( completion, labelSet )
抽象操作 LoopContinues 接受参数 completion（一个
- 如果 completion 是一个
normal completion ，返回true 。 - 如果 completion 不是一个
continue completion ，返回false 。 - 如果 completion.[[Target]]
是
empty ，返回true 。 - 如果 labelSet 包含 completion.[[Target]]，返回
true 。 - 返回
false 。
在
14.7.1.2 运行时语义：LoopEvaluation
语法导向操作 LoopEvaluation 接受参数 labelSet（一个
- 返回 ?
DoWhileLoopEvaluation ofDoWhileStatement with argument labelSet.
- 返回 ?
WhileLoopEvaluation ofWhileStatement with argument labelSet.
- 返回 ?
ForLoopEvaluation ofForStatement with argument labelSet.
- 返回 ?
ForInOfLoopEvaluation ofForInOfStatement with argument labelSet.
14.7.2 do-while 语句
语法
14.7.2.1 静态语义：早期错误
-
如果
IsLabelledFunction (Statement ) 是true ，则为语法错误。
只有在实现
14.7.2.2 运行时语义：DoWhileLoopEvaluation
语法导向操作 DoWhileLoopEvaluation 接受参数 labelSet（一个
- 设 V 为
undefined 。 - 重复，
- 设 stmtResult 为
Completion (求值 ofStatement )。 - 如果
LoopContinues (stmtResult, labelSet) 是false ，返回 ?UpdateEmpty (stmtResult, V)。 - 如果 stmtResult.[[Value]]
不是
empty ，设 V 为 stmtResult.[[Value]]。 - 设 exprRef 为 ?
求值 ofExpression 。 - 设 exprValue 为 ?
GetValue (exprRef)。 - 如果
ToBoolean (exprValue) 是false ，返回 V。
- 设 stmtResult 为
14.7.3 while 语句
语法
14.7.3.1 静态语义：早期错误
-
如果
IsLabelledFunction (Statement ) 是true ，则为语法错误。
只有在实现
14.7.3.2 运行时语义：WhileLoopEvaluation
语法导向操作 WhileLoopEvaluation 接受参数 labelSet（一个
- 设 V 为
undefined 。 - 重复，
- 设 exprRef 为 ?
求值 ofExpression 。 - 设 exprValue 为 ?
GetValue (exprRef)。 - 如果
ToBoolean (exprValue) 是false ，返回 V。 - 设 stmtResult 为
Completion (求值 ofStatement )。 - 如果
LoopContinues (stmtResult, labelSet) 是false ，返回 ?UpdateEmpty (stmtResult, V)。 - 如果 stmtResult.[[Value]]
不是
empty ，设 V 为 stmtResult.[[Value]]。
- 设 exprRef 为 ?
14.7.4 for 语句
语法
14.7.4.1 静态语义：早期错误
-
如果
IsLabelledFunction (Statement ) 是true ，则为语法错误。
只有在实现
-
如果
BoundNames ofLexicalDeclaration 中的任何元素也出现在VarDeclaredNames ofStatement 中，则为语法错误。
14.7.4.2 运行时语义：ForLoopEvaluation
语法导向操作 ForLoopEvaluation 接受参数 labelSet（一个
- 如果第一个
Expression 存在，则- 设 exprRef 为 ?
求值 of the firstExpression 。 - 执行 ?
GetValue (exprRef)。
- 设 exprRef 为 ?
- 如果第二个
Expression 存在，设 test 为第二个Expression ；否则，设 test 为empty 。 - 如果第三个
Expression 存在，设 increment 为第三个Expression ；否则，设 increment 为empty 。 - 返回 ?
ForBodyEvaluation (test, increment,Statement , « », labelSet)。
- 执行 ?
求值 ofVariableDeclarationList 。 - 如果第一个
Expression 存在，设 test 为第一个Expression ；否则，设 test 为empty 。 - 如果第二个
Expression 存在，设 increment 为第二个Expression ；否则，设 increment 为empty 。 - 返回 ?
ForBodyEvaluation (test, increment,Statement , « », labelSet)。
- 设 oldEnv 为
运行执行上下文 的词法环境。 - 设 loopEnv 为
NewDeclarativeEnvironment (oldEnv)。 - 设 isConst 为
IsConstantDeclaration ofLexicalDeclaration 。 - 设 boundNames 为
BoundNames ofLexicalDeclaration 。 - 对于 boundNames 的每个元素 dn，执行
- 如果 isConst 是
true ，则- 执行
! loopEnv.CreateImmutableBinding(dn,
true )。
- 执行
! loopEnv.CreateImmutableBinding(dn,
- 否则，
- 执行
! loopEnv.CreateMutableBinding(dn,
false )。
- 执行
! loopEnv.CreateMutableBinding(dn,
- 如果 isConst 是
- 将
运行执行上下文 的词法环境设置为 loopEnv。 - 设 forDcl 为
Completion (求值 ofLexicalDeclaration )。 - 如果 forDcl 是一个
abrupt completion ，则- 将
运行执行上下文 的词法环境设置为 oldEnv。 - 返回 ? forDcl。
- 将
- 如果 isConst 是
false ，设 perIterationLets 为 boundNames；否则设 perIterationLets 为 一个新的空List 。 - 如果第一个
Expression 存在，设 test 为第一个Expression ；否则，设 test 为empty 。 - 如果第二个
Expression 存在，设 increment 为第二个Expression ；否则，设 increment 为empty 。 - 设 bodyResult 为
Completion (ForBodyEvaluation (test, increment,Statement , perIterationLets, labelSet))。 - 将
运行执行上下文 的词法环境设置为 oldEnv。 - 返回 ? bodyResult。
14.7.4.3 ForBodyEvaluation ( test, increment, stmt, perIterationBindings, labelSet )
抽象操作 ForBodyEvaluation 接受参数 test（一个
- 设 V 为
undefined 。 - 执行 ?
CreatePerIterationEnvironment (perIterationBindings)。 - 重复，
- 如果 test 不是
empty ，则 - 设 result 为
Completion (求值 of stmt)。 - 如果
LoopContinues (result, labelSet) 是false ，返回 ?UpdateEmpty (result, V)。 - 如果 result.[[Value]]
不是
empty ，设 V 为 result.[[Value]]。 - 执行 ?
CreatePerIterationEnvironment (perIterationBindings)。 - 如果 increment 不是
empty ，则
- 如果 test 不是
14.7.4.4 CreatePerIterationEnvironment ( perIterationBindings )
抽象操作 CreatePerIterationEnvironment 接受参数 perIterationBindings
（一个
- 如果 perIterationBindings 有任何元素，则
- 设 lastIterationEnv 为
运行执行上下文 的词法环境。 - 设 outer 为 lastIterationEnv.[[OuterEnv]]。
断言 ：outer 不是null 。- 设 thisIterationEnv 为
NewDeclarativeEnvironment (outer)。 - 对于 perIterationBindings 的每个元素 bn，执行
- 执行
! thisIterationEnv.CreateMutableBinding(bn,
false )。 - 设 lastValue 为
? lastIterationEnv.GetBindingValue(bn,
true )。 - 执行 ! thisIterationEnv.InitializeBinding(bn, lastValue)。
- 执行
! thisIterationEnv.CreateMutableBinding(bn,
- 将
运行执行上下文 的词法环境设置为 thisIterationEnv。
- 设 lastIterationEnv 为
- 返回
unused 。
14.7.5 for-in、for-of 和
for-await-of 语句
语法
本节由附录
14.7.5.1 静态语义：早期错误
-
如果
IsLabelledFunction (Statement ) 是true ，则为语法错误。
只有在实现
如果
如果
-
如果
AssignmentTargetType 的LeftHandSideExpression 不是simple ，则为语法错误。
-
如果
BoundNames ofForDeclaration 包含"let" ，则为语法错误。 -
如果
BoundNames ofForDeclaration 中的任何元素也出现在VarDeclaredNames ofStatement 中，则为语法错误。 -
如果
BoundNames ofForDeclaration 包含任何重复条目，则为语法错误。
14.7.5.2 静态语义：IsDestructuring
语法导向操作 IsDestructuring 不接受参数并返回一个布尔值。它在以下产生式上定义：
- 如果
PrimaryExpression 是ObjectLiteral 或ArrayLiteral ， 返回true 。 - 返回
false 。
- 返回
false 。
- 返回
IsDestructuring ofForBinding 。
- 返回
false 。
- 返回
true 。
本节由附录
14.7.5.3 运行时语义：ForDeclarationBindingInitialization
语法导向操作 ForDeclarationBindingInitialization 接受参数 value（一个
它在以下产生式上定义：
- 返回 ?
BindingInitialization ofForBinding with arguments value and environment。
14.7.5.4 运行时语义：ForDeclarationBindingInstantiation
语法导向操作 ForDeclarationBindingInstantiation 接受参数 environment（一个
- 对于
BoundNames ofForBinding 的每个元素 name，执行- 如果
IsConstantDeclaration ofLetOrConst 是true ，则- 执行
! environment.CreateImmutableBinding(name,
true )。
- 执行
! environment.CreateImmutableBinding(name,
- 否则，
- 执行
! environment.CreateMutableBinding(name,
false )。
- 执行
! environment.CreateMutableBinding(name,
- 如果
- 返回
unused 。
14.7.5.5 运行时语义：ForInOfLoopEvaluation
语法导向操作 ForInOfLoopEvaluation 接受参数 labelSet（一个
- 设 keyResult 为 ?
ForIn/OfHeadEvaluation (« »,Expression ,enumerate )。 - 返回 ?
ForIn/OfBodyEvaluation (LeftHandSideExpression ,Statement , keyResult,enumerate ,assignment , labelSet)。
- 设 keyResult 为 ?
ForIn/OfHeadEvaluation (« »,Expression ,enumerate )。 - 返回 ?
ForIn/OfBodyEvaluation (ForBinding ,Statement , keyResult,enumerate ,var-binding , labelSet)。
- 设 keyResult 为 ?
ForIn/OfHeadEvaluation (BoundNames ofForDeclaration ,Expression ,enumerate )。 - 返回 ?
ForIn/OfBodyEvaluation (ForDeclaration ,Statement , keyResult,enumerate ,lexical-binding , labelSet)。
- 设 keyResult 为 ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,iterate )。 - 返回 ?
ForIn/OfBodyEvaluation (LeftHandSideExpression ,Statement , keyResult,iterate ,assignment , labelSet)。
- 设 keyResult 为 ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,iterate )。 - 返回 ?
ForIn/OfBodyEvaluation (ForBinding ,Statement , keyResult,iterate ,var-binding , labelSet)。
- 设 keyResult 为 ?
ForIn/OfHeadEvaluation (BoundNames ofForDeclaration ,AssignmentExpression ,iterate )。 - 返回 ?
ForIn/OfBodyEvaluation (ForDeclaration ,Statement , keyResult,iterate ,lexical-binding , labelSet)。
- 设 keyResult 为 ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,async-iterate )。 - 返回 ?
ForIn/OfBodyEvaluation (LeftHandSideExpression ,Statement , keyResult,iterate ,assignment , labelSet,async )。
- 设 keyResult 为 ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,async-iterate )。 - 返回 ?
ForIn/OfBodyEvaluation (ForBinding ,Statement , keyResult,iterate ,var-binding , labelSet,async )。
- 设 keyResult 为 ?
ForIn/OfHeadEvaluation (BoundNames ofForDeclaration ,AssignmentExpression ,async-iterate )。 - 返回 ?
ForIn/OfBodyEvaluation (ForDeclaration ,Statement , keyResult,iterate ,lexical-binding , labelSet,async )。
本节由附录
14.7.5.6 ForIn/OfHeadEvaluation ( uninitializedBoundNames, expr, iterationKind )
抽象操作 ForIn/OfHeadEvaluation 接受参数 uninitializedBoundNames（一个
- 令 oldEnv 为
运行执行上下文 的词法环境。 - 如果 uninitializedBoundNames 不为空，则
断言 ： uninitializedBoundNames 没有重复条目。- 令 newEnv 为
NewDeclarativeEnvironment (oldEnv)。 - 对于 uninitializedBoundNames 中的每个字符串
name，执行
- 执行
! newEnv.CreateMutableBinding(name,
false )。
- 执行
! newEnv.CreateMutableBinding(name,
- 将
运行执行上下文 的词法环境设置为 newEnv。
- 令 exprRef 为
Completion (Evaluation of expr)。 - 将
运行执行上下文 的词法环境设置为 oldEnv。 - 令 exprValue 为 ?
GetValue (? exprRef)。 - 如果 iterationKind 是
enumerate ，则- 如果 exprValue 是
undefined 或null ，则- 返回
完成记录 { [[Type]]:break , [[Value]]:empty , [[Target]]:empty }。
- 返回
- 令 obj 为 !
ToObject (exprValue)。 - 令 iterator 为
EnumerateObjectProperties (obj)。 - 令 nextMethod 为 !
GetV (iterator,"next" )。 - 返回
迭代器记录 { [[Iterator]]: iterator, [[NextMethod]]: nextMethod, [[Done]]:false }。
- 如果 exprValue 是
- 否则
断言 ：iterationKind 是iterate 或async-iterate 。- 如果 iterationKind 是
async-iterate ，令 iteratorKind 为async 。 - 否则，令 iteratorKind 为
sync 。 - 返回 ?
GetIterator (exprValue, iteratorKind)。
14.7.5.7 ForIn/OfBodyEvaluation ( lhs, stmt, iteratorRecord, iterationKind, lhsKind, labelSet [ , iteratorKind ] )
抽象操作 ForIn/OfBodyEvaluation 接受参数 lhs（一个
- 如果 iteratorKind 不存在，设置
iteratorKind 为
sync 。 - 令 oldEnv 为
运行执行上下文 的词法环境。 - 令 V 为
undefined 。 - 令 destructuring 为
IsDestructuring 的 lhs。 - 如果 destructuring 为
true 且 lhsKind 为assignment ，则断言 ：lhs 是一个LeftHandSideExpression 。- 令 assignmentPattern 为
AssignmentPattern 的覆盖 的 lhs。
- 重复，
- 令 nextResult 为 ?
Call (iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]])。 - 如果 iteratorKind 是
async ， 设置 nextResult 为 ?Await (nextResult)。 - 如果 nextResult
不是一个 Object ，抛出一个TypeError 异常。 - 令 done 为 ?
IteratorComplete (nextResult)。 - 如果 done 是
true ，返回 V。 - 令 nextValue 为 ?
IteratorValue (nextResult)。 - 如果 lhsKind 是
assignment 或var-binding ，则- 如果 destructuring 是
true ， 则- 如果 lhsKind 是
assignment ，则- 令 status 为
Completion (DestructuringAssignmentEvaluation of assignmentPattern with argument nextValue)。
- 令 status 为
- 否则，
断言 ： lhsKind 是var-binding 。断言 ：lhs 是一个ForBinding 。- 令 status 为
Completion (BindingInitialization of lhs 使用 参数 nextValue 和undefined )。
- 如果 lhsKind 是
- 否则，
- 令 lhsRef 为
Completion (Evaluation of lhs)。（可能会被 多次评估。） - 如果 lhsRef 是一个
异常 完成 ，则- 令 status 为 lhsRef。
- 否则，
- 令 status 为
Completion (PutValue (lhsRef.[[Value]], nextValue))。
- 令 status 为
- 令 lhsRef 为
- 如果 destructuring 是
- 否则，
断言 ：lhsKind 是lexical-binding 。断言 ：lhs 是一个ForDeclaration 。- 令 iterationEnv 为
NewDeclarativeEnvironment (oldEnv)。 - 执行
ForDeclarationBindingInstantiation 的 lhs 使用参数 iterationEnv。 - 设置
运行 执行上下文 的词法环境为 iterationEnv。 - 如果 destructuring 是
true ， 则- 令 status 为
Completion (ForDeclarationBindingInitialization of lhs 使用参数 nextValue 和 iterationEnv)。
- 令 status 为
- 否则，
断言 ：lhs 绑定一个单一的名称。- 令 lhsName 为
BoundNames 的 lhs 的唯一元素。 - 令 lhsRef 为 !
ResolveBinding (lhsName)。 - 令 status 为
Completion (InitializeReferencedBinding (lhsRef, nextValue))。
- 如果 status 是一个
异常 完成 ，则- 设置
运行 执行上下文 的词法环境为 oldEnv。 - 如果 iteratorKind 是
async ，返回 ?AsyncIteratorClose (iteratorRecord, status)。 - 如果 iterationKind 是
enumerate ，则- 返回 ? status。
- 否则，
断言 ： iterationKind 是iterate 。- 返回 ?
IteratorClose (iteratorRecord, status)。
- 设置
- 令 result 为
Completion (Evaluation of stmt)。 - 设置
运行 执行上下文 的词法环境为 oldEnv。 - 如果
LoopContinues (result, labelSet) 是false ，则- 如果 iterationKind 是
enumerate ，则- 返回 ?
UpdateEmpty (result, V)。
- 返回 ?
- 否则，
断言 ： iterationKind 是iterate 。- 设置 status 为
Completion (UpdateEmpty (result, V))。 - 如果 iteratorKind 是
async ，返回 ?AsyncIteratorClose (iteratorRecord, status)。 - 返回 ?
IteratorClose (iteratorRecord, status)。
- 如果 iterationKind 是
- 如果 result.[[Value]]
不是
empty ，设置 V 为 result.[[Value]]。
- 令 nextResult 为 ?
14.7.5.8 运行时语义：评估
- 令 bindingId 为
StringValue 的BindingIdentifier 。 - 返回 ?
ResolveBinding (bindingId)。
14.7.5.9 EnumerateObjectProperties ( O )
抽象操作 EnumerateObjectProperties 接受参数 O（一个对象）并返回一个迭代器。它在调用时执行以下步骤：
- 返回一个迭代器对象（
27.1.1.2 ），其next方法遍历 O 的所有可枚举的字符串键属性。迭代器对象对 ECMAScript 代码永远不可直接访问。遍历属性的机制和顺序未指定，但必须符合以下规则。
迭代器的 throw 和 return 方法是 next 方法处理对象属性以确定属性键是否应作为迭代器值返回。返回的属性键不包括 Symbols。目标对象的属性可能在枚举期间被删除。在迭代器的 next
方法处理之前删除的属性将被忽略。如果在枚举期间向目标对象添加新属性，则不能保证新添加的属性会在活动枚举中被处理。一个属性名在任何枚举中最多由迭代器的 next 方法返回一次。
枚举目标对象的属性包括枚举其原型及其原型的原型等的属性，递归地；但如果原型的属性与迭代器的 next 方法已经处理的属性同名，则不处理原型的属性。原型对象的可枚举属性名必须通过调用
EnumerateObjectProperties 并将原型对象作为参数来获取。EnumerateObjectProperties 必须通过调用目标对象的 [[OwnPropertyKeys]] 内部方法来获取目标对象的自有属性键。目标对象的属性属性必须通过调用其 [[GetOwnProperty]] 内部方法来获取。
此外，如果 O 或其原型链中的任何对象不是
- O 或其原型链中的对象的 [[Prototype]] 内部槽的值发生变化，
- O 或其原型链中的对象的属性被删除，
- O 的原型链中的对象的属性被添加，或
- O 或其原型链中的对象的属性的 [[Enumerable]] 属性发生变化。
ECMAScript 实现不需要直接实现
以下是一个符合这些规则的 ECMAScript 生成器函数的非正式定义：
function* EnumerateObjectProperties(obj) {
const visited = new Set();
for (const key of Reflect.ownKeys(obj)) {
if (typeof key === "symbol") continue;
const desc = Reflect.getOwnPropertyDescriptor(obj, key);
if (desc) {
visited.add(key);
if (desc.enumerable) yield key;
}
}
const proto = Reflect.getPrototypeOf(obj);
if (proto === null) return;
for (const protoKey of EnumerateObjectProperties(proto)) {
if (!visited.has(protoKey)) yield protoKey;
}
}14.7.5.10 For-In 迭代器对象
For-In 迭代器是表示特定对象上的特定迭代的对象。For-In 迭代器对象永远不会直接对 ECMAScript 代码可访问；它们仅存在于阐明
14.7.5.10.1 CreateForInIterator ( object )
抽象操作 CreateForInIterator 接受参数 object（一个对象）并返回一个 For-In 迭代器。它用于创建一个 For-In 迭代器对象，该对象按特定顺序迭代 object 的自身和继承的可枚举字符串属性。调用时执行以下步骤：
- 令 iterator 为
OrdinaryObjectCreate (%ForInIteratorPrototype% , « [[Object]], [[ObjectWasVisited]], [[VisitedKeys]], [[RemainingKeys]] »)。 - 将 iterator.[[Object]] 设置为 object。
- 将 iterator.[[ObjectWasVisited]] 设置为
false 。 - 将 iterator.[[VisitedKeys]]
设置为一个新的空
列表 。 - 将 iterator.[[RemainingKeys]] 设置为一个新的空
列表 。 - 返回 iterator。
14.7.5.10.2 %ForInIteratorPrototype% 对象
%ForInIteratorPrototype% 对象：
- 具有所有 For-In 迭代器对象继承的属性。
- 是一个
普通对象 。 - 有一个内部槽 [[Prototype]]，其值是
%IteratorPrototype% 。 - 永远不能被 ECMAScript 代码直接访问。
- 具有以下属性：
14.7.5.10.2.1 %ForInIteratorPrototype%.next ( )
- 令 O 为
this 值。 断言 ：O 是一个对象 。断言 ：O 具有 For-In 迭代器实例的所有内部槽 (14.7.5.10.3 )。- 令 object 为 O.[[Object]]。
- 重复，
- 如果 O.[[ObjectWasVisited]] 为
false ，则- 令 keys 为 ? object.[[OwnPropertyKeys]]()。
- 对 keys 的每个元素 key，执行
- 如果 key 是一个
字符串 ，则- 将 key 追加到 O.[[RemainingKeys]]。
- 如果 key 是一个
- 将 O.[[ObjectWasVisited]] 设置为
true 。
- 重复，直到 O.[[RemainingKeys]] 为空，
- 令 r 为 O.[[RemainingKeys]] 的第一个元素。
- 从 O.[[RemainingKeys]] 中移除第一个元素。
- 如果 O.[[VisitedKeys]] 中不存在一个元素 v 使得
SameValue (r, v) 为true ，则- 令 desc 为 ? object.[[GetOwnProperty]](r)。
- 如果 desc 不为
undefined ，则- 将 r 追加到 O.[[VisitedKeys]]。
- 如果 desc.[[Enumerable]] 为
true ，返回CreateIterResultObject (r,false )。
- 将 object 设置为 ? object.[[GetPrototypeOf]]()。
- 将 O.[[Object]] 设置为 object。
- 将 O.[[ObjectWasVisited]] 设置为
false 。 - 如果 object 为
null ，返回CreateIterResultObject (undefined ,true )。
- 如果 O.[[ObjectWasVisited]] 为
14.7.5.10.3 For-In 迭代器实例的属性
For-In 迭代器实例是
14.8 continue 语句
语法
14.8.1 静态语义：早期错误
-
如果这个
ContinueStatement 不是嵌套在一个IterationStatement 内（直接或间接，但不跨函数或static初始化块边界），则是语法错误。
14.8.2 运行时语义：求值
- 返回
完成记录 { [[Type]]:continue , [[Value]]:empty , [[Target]]:empty }.
- 令 label 为
StringValue 的LabelIdentifier 。 - 返回
完成记录 { [[Type]]:continue , [[Value]]:empty , [[Target]]: label }.
14.9 break 语句
语法
14.9.1 静态语义：早期错误
-
如果这个
BreakStatement 不是嵌套在一个IterationStatement 或一个SwitchStatement 内（直接或间接，但不跨函数或static初始化块边界），则是语法错误。
14.9.2 运行时语义：求值
- 返回
完成记录 { [[Type]]:break , [[Value]]:empty , [[Target]]:empty }.
- 令 label 为
StringValue 的LabelIdentifier 。 - 返回
完成记录 { [[Type]]:break , [[Value]]:empty , [[Target]]: label }.
14.10 return 语句
语法
return 语句会导致函数停止执行，并在大多数情况下返回一个值给调用者。如果省略了
return 语句可能实际上不会返回值给调用者。例如，在
try 块中，return 语句的
finally 块时被另一个
14.10.1 运行时语义：求值
-
返回
Completion Record { [[Type]]:return , [[Value]]:undefined , [[Target]]:empty }.
-
令 exprRef 为 ?
Evaluation 的Expression 。 -
令 exprValue 为 ?
GetValue (exprRef)。 -
如果
GetGeneratorKind () 是async ，设置 exprValue 为 ?Await (exprValue)。 -
返回
Completion Record { [[Type]]:return , [[Value]]: exprValue, [[Target]]:empty }.
14.11 with 语句
语法
with 语句为计算对象添加了一个
14.11.1 静态语义：早期错误
-
如果此产生式匹配的
源文本 包含在严格模式代码 中，则这是一个语法错误。 -
如果
IsLabelledFunction (Statement ) 是true ，则这是一个语法错误。
仅在实现
14.11.2 运行时语义：求值
-
令 val 为 ?
Evaluation 的Expression 。 -
令 obj 为 ?
ToObject (?GetValue (val))。 -
令 oldEnv 为当前执行上下文的
词法环境 。 -
令 newEnv 为
NewObjectEnvironment (obj,true , oldEnv)。 -
将当前执行上下文的
词法环境 设置为 newEnv。 -
令 C 为
Completion (Evaluation 的Statement )。 -
将当前执行上下文的
词法环境 设置回 oldEnv。 -
返回 ?
UpdateEmpty (C,undefined )。
14.12 switch 语句
语法
14.12.1 静态语义：早期错误
-
如果
CaseBlock 的LexicallyDeclaredNames 包含任何重复条目，则这是一个语法错误。 -
如果
CaseBlock 的任何元素在VarDeclaredNames 中也出现，则这是一个语法错误。
14.12.2 运行时语义：CaseBlockEvaluation
- 返回
undefined 。
- 令 V 为
undefined 。 - 令 A 为
List 中的CaseClause 项，按源文本顺序排列。 - 令 found 为
false 。 - 对 A 中的每个
CaseClause C，执行以下操作：-
如果 found 为
false ，则：-
令 found 为 ?
CaseClauseIsSelected (C, input)。
-
令 found 为 ?
-
如果 found 为
true ，则：-
令 R 为
Completion (Evaluation (C))。 -
如果 R.[[Value]] 不是
empty ，则将 V 设为 R.[[Value]]。 -
如果 R 是
中止完成 ，则返回 ?UpdateEmpty (R, V)。
-
令 R 为
-
如果 found 为
- 返回 V。
- 令 V 为
undefined 。 - 如果存在第一个
CaseClauses ，则：-
令 A 为
List 中的CaseClause 项，按源文本顺序排列。
-
令 A 为
-
否则：
-
令 A 为一个新的空
List 。
-
令 A 为一个新的空
- 令 found 为
false 。 - 对 A 中的每个
CaseClause C，执行以下操作：-
如果 found 为
false ，则：-
令 found 为 ?
CaseClauseIsSelected (C, input)。
-
令 found 为 ?
-
如果 found 为
true ，则：-
令 R 为
Completion (Evaluation (C))。 -
如果 R.[[Value]] 不是
empty ，则将 V 设为 R.[[Value]]。 -
如果 R 是
中止完成 ，则返回 ?UpdateEmpty (R, V)。
-
令 R 为
-
如果 found 为
- 令 foundInB 为
false 。 - 如果存在第二个
CaseClauses ，则：-
令 B 为
List 中的CaseClause 项，按源文本顺序排列。
-
令 B 为
-
否则：
-
令 B 为一个新的空
List 。
-
令 B 为一个新的空
-
如果 found 为
false ，则：-
对 B 中的每个
CaseClause C，执行以下操作：-
如果 foundInB 为
false ，则：-
令 foundInB 为 ?
CaseClauseIsSelected (C, input)。
-
令 foundInB 为 ?
-
如果 foundInB 为
true ，则：-
令 R 为
Completion (Evaluation (CaseClause C))。 -
如果 R.[[Value]] 不是
empty ，则将 V 设为 R.[[Value]]。 -
如果 R 是
中止完成 ，则返回 ?UpdateEmpty (R, V)。
-
令 R 为
-
如果 foundInB 为
-
对 B 中的每个
- 如果 foundInB 为
true ，则返回 V。 -
令 defaultR 为
Completion (Evaluation (DefaultClause ))。 -
如果 defaultR.[[Value]] 不是
empty ，则将 V 设为 defaultR.[[Value]]。 -
如果 defaultR 是
中止完成 ，则返回 ?UpdateEmpty (defaultR, V)。 -
注：以下是第二个
CaseClauses 的另一个完整迭代。 -
对 B 中的每个
CaseClause C，执行以下操作：-
令 R 为
Completion (Evaluation (CaseClause C))。 -
如果 R.[[Value]] 不是
empty ，则将 V 设为 R.[[Value]]。 -
如果 R 是
中止完成 ，则返回 ?UpdateEmpty (R, V)。
-
令 R 为
- 返回 V。
14.12.3 CaseClauseIsSelected ( C, input )
抽象操作 CaseClauseIsSelected 接受参数 C（一个
-
断言 ：C 是CaseClause : case Expression : StatementList opt -
令 exprRef 为 ?
Evaluation C 的Expression 。 -
令 clauseSelector 为 ?
GetValue (exprRef)。 -
返回
IsStrictlyEqual (input, clauseSelector)。
此操作不执行 C 的
14.12.4 运行时语义：Evaluation
-
令 exprRef 为 ?
Evaluation (Expression )。 -
令 switchValue 为 ?
GetValue (exprRef)。 -
令 oldEnv 为
当前执行上下文 的 LexicalEnvironment。 -
令 blockEnv 为
NewDeclarativeEnvironment (oldEnv)。 -
执行
BlockDeclarationInstantiation (CaseBlock , blockEnv)。 -
将
当前执行上下文 的 LexicalEnvironment 设置为 blockEnv。 -
令 R 为
Completion (CaseBlockEvaluation (CaseBlock , switchValue))。 -
将
当前执行上下文 的 LexicalEnvironment 设置回 oldEnv。 - 返回 R。
无论控制如何离开
- 返回
empty 。
-
返回 ?
Evaluation (StatementList )。
- 返回
empty 。
-
返回 ?
Evaluation (StatementList )。
14.13 带标签的语句
语法
一个 break和continue语句结合使用。ECMAScript
没有goto语句。
一个
14.13.1 静态语义：早期错误
- 如果此生成的源文本匹配任何源文本，则为语法错误。
如果实现了
14.13.2 静态语义：IsLabelledFunction (stmt)
抽象操作 IsLabelledFunction 接受参数 stmt (一个
- 如果 stmt 不是一个
LabelledStatement ，返回false 。 - 让 item 成为 stmt 的
LabelledItem 。 - 如果 item 是
LabelledItem : FunctionDeclaration true 。 - 让 subStmt 成为 item 的
Statement 。 - 返回
IsLabelledFunction (subStmt)。
14.13.3 运行时语义：评估
- 返回 ?
LabelledEvaluation 的这个LabelledStatement ，参数为 « »。
14.13.4 运行时语义：LabelledEvaluation
- 让 stmtResult 成为
Completion (LoopEvaluation 的IterationStatement ，参数为 labelSet)。 - 如果 stmtResult 是一个
break completion ，则- 如果 stmtResult.[[Target]] 是
empty ，则- 如果 stmtResult.[[Value]]
是
empty ，则将 stmtResult 设置为NormalCompletion (undefined )。 - 否则，将 stmtResult 设置为
NormalCompletion (stmtResult.[[Value]])。
- 如果 stmtResult.[[Value]]
是
- 如果 stmtResult.[[Target]] 是
- 返回 ? stmtResult。
- 让 stmtResult 成为
Completion (Evaluation 的SwitchStatement )。 - 如果 stmtResult 是一个
break completion ，则- 如果 stmtResult.[[Target]] 是
empty ，则- 如果 stmtResult.[[Value]]
是
empty ，则将 stmtResult 设置为NormalCompletion (undefined )。 - 否则，将 stmtResult 设置为
NormalCompletion (stmtResult.[[Value]])。
- 如果 stmtResult.[[Value]]
是
- 如果 stmtResult.[[Target]] 是
- 返回 ? stmtResult。
一个
- 让 label 成为
StringValue 的LabelIdentifier 。 - 让 newLabelSet 成为
列表连接 的 labelSet 和 « label »。 - 让 stmtResult 成为
Completion (LabelledEvaluation 的LabelledItem ，参数为 newLabelSet)。 - 如果 stmtResult 是一个
break completion 并且 stmtResult.[[Target]] 是 label，则- 将 stmtResult 设置为
NormalCompletion (stmtResult.[[Value]])。
- 将 stmtResult 设置为
- 返回 ? stmtResult。
- 返回 ?
Evaluation 的FunctionDeclaration 。
- 返回 ?
Evaluation 的Statement 。
14.14 throw 语句
语法
14.14.1 运行时语义：求值
- 令 exprRef 为 ?
Evaluation 的表达式。 - 令 exprValue 为 ?
GetValue (exprRef)。 - 返回
ThrowCompletion (exprValue)。
14.15 try 语句
语法
try 语句包含可能发生异常的代码块，如运行时错误或 throw 语句。catch 子句提供异常处理代码。当 catch 子句捕获异常时，其
14.15.1 静态语义：早期错误
-
如果
BoundNames 中的CatchParameter 包含任何重复元素，则为语法错误。 -
如果
BoundNames 中的任何元素也出现在LexicallyDeclaredNames 的Block 中，则为语法错误。 -
如果
BoundNames 中的任何元素也出现在VarDeclaredNames 的Block 中，则为语法错误。
对于此生成规则的替代静态语义定义，见
14.15.2 运行时语义：CatchClauseEvaluation
CatchClauseEvaluation 是一个带有参数 thrownValue（一个 ECMAScript 语言值）的语法直接操作，返回一个包含 ECMAScript 语言值的正常完成记录或一个中断完成记录。它在以下生成规则中定义：
- 令 oldEnv 为当前执行上下文的 LexicalEnvironment。
- 令 catchEnv 为
NewDeclarativeEnvironment (oldEnv)。 - 对于
BoundNames 的CatchParameter 中的每个元素 argName，执行- 执行
! catchEnv.CreateMutableBinding(argName,
false )。
- 执行
! catchEnv.CreateMutableBinding(argName,
- 将当前执行上下文的 LexicalEnvironment 设置为 catchEnv。
- 令 status 为
Completion (BindingInitialization 的CatchParameter ，参数为 thrownValue 和 catchEnv)。 - 如果 status 是一个中断完成，则
- 将当前执行上下文的 LexicalEnvironment 设置为 oldEnv。
- 返回 ? status。
- 令 B 为
Completion (Evaluation 的Block )。 - 将当前执行上下文的 LexicalEnvironment 设置为 oldEnv。
- 返回 ? B。
- 返回 ?
Evaluation 的Block 。
无论控制如何离开
14.15.3 运行时语义：Evaluation
- 令 B 为
Completion (Evaluation 的Block )。 - 如果 B 是一个
throw completion ，令 C 为Completion (CatchClauseEvaluation 的Catch ，参数为 B.[[Value]])。 - 否则，令 C 为 B。
- 返回 ?
UpdateEmpty (C,undefined )。
- 令 B 为
Completion (Evaluation 的Block )。 - 令 F 为
Completion (Evaluation 的Finally )。 - 如果 F 是一个
normal completion ，则将 F 设置为 B。 - 返回 ?
UpdateEmpty (F,undefined )。
- 令 B 为
Completion (Evaluation 的Block )。 - 如果 B 是一个
throw completion ，令 C 为Completion (CatchClauseEvaluation 的Catch ，参数为 B.[[Value]])。 - 否则，令 C 为 B。
- 令 F 为
Completion (Evaluation 的Finally )。 - 如果 F 是一个
normal completion ，则将 F 设置为 C。 - 返回 ?
UpdateEmpty (F,undefined )。
14.16 debugger 语句
句法
14.16.1 运行时语义：Evaluation
执行
- 如果一个
实现定义 的调试设施可用且已启用，则- 执行一个
实现定义 的调试动作。 - 返回一个新的
实现定义 的Completion Record 。
- 执行一个
- 否则，
- 返回
empty 。
- 返回
15 ECMAScript 语言：函数和类
各种 ECMAScript 语言元素会导致创建 ECMAScript
15.1 参数列表
语法
15.1.1 静态语义：早期错误
-
如果
BoundNames 中包含FormalParameters 的任何重复元素，则这是一个语法错误。
-
如果
IsSimpleParameterList 是false ，并且BoundNames 中包含FormalParameterList 的任何重复元素，则这是一个语法错误。
在
15.1.2 静态语义：ContainsExpression
- 返回
false 。
- 返回
false 。
- 令 has 为
ContainsExpression 的BindingElementList 。 - 如果 has 为
true ，则返回true 。 - 返回
ContainsExpression 的BindingRestElement 。
- 令 has 为
ContainsExpression 的BindingPropertyList 。 - 如果 has 为
true ，则返回true 。 - 返回
ContainsExpression 的BindingProperty 。
- 令 has 为
ContainsExpression 的BindingElementList 。 - 如果 has 为
true ，则返回true 。 - 返回
ContainsExpression 的BindingElisionElement 。
- 令 has 为
IsComputedPropertyKey 的PropertyName 。 - 如果 has 为
true ，则返回true 。 - 返回
ContainsExpression 的BindingElement 。
- 返回
true 。
- 返回
false 。
- 返回
true 。
- 返回
false 。
- 返回
false 。
- 如果
ContainsExpression 的FormalParameterList 为true ，则返回true 。 - 返回
ContainsExpression 的FunctionRestParameter 。
- 如果
ContainsExpression 的FormalParameterList 为true ，则返回true 。 - 返回
ContainsExpression 的FormalParameter 。
- 返回
false 。
- 令 formals 为
ArrowFormalParameters ，它被涵盖 的CoverParenthesizedExpressionAndArrowParameterList 。 - 返回
ContainsExpression 的 formals。
- 返回
false 。
15.1.3 静态语义：IsSimpleParameterList
- 返回
false 。
- 返回
false 。
- 返回
true 。
- 返回
false 。
- 返回
true 。
- 返回
false 。
- 返回
false 。
- 如果
IsSimpleParameterList 的FormalParameterList 为false ，则返回false 。 - 返回
IsSimpleParameterList 的FormalParameter 。
- 返回
true 。
- 令 formals 为
ArrowFormalParameters ，它被涵盖 的CoverParenthesizedExpressionAndArrowParameterList 。 - 返回
IsSimpleParameterList 的 formals。
- 返回
true 。
- 令 head 为
AsyncArrowHead ，它被涵盖 的CoverCallExpressionAndAsyncArrowHead 。 - 返回
IsSimpleParameterList 的 head。
15.1.4 静态语义：HasInitializer
- 返回
false 。
- 返回
true 。
- 返回
false 。
- 返回
true 。
- 如果
HasInitializer 的FormalParameterList 为true ，则返回true 。 - 返回
HasInitializer 的FormalParameter 。
15.1.5 静态语义：ExpectedArgumentCount
- 返回 0。
- 如果
HasInitializer 的FormalParameter 为true ，返回 0。 - 返回 1。
- 令 count 为
ExpectedArgumentCount 的FormalParameterList 。 - 如果
HasInitializer 的FormalParameterList 为true 或者HasInitializer 的FormalParameter 为true ，则返回 count。 - 返回 count + 1。
- 返回 1。
- 令 formals 为
ArrowFormalParameters ，它被涵盖 的CoverParenthesizedExpressionAndArrowParameterList 。 - 返回
ExpectedArgumentCount 的 formals。
- 如果
HasInitializer 的FormalParameter 为true ，返回 0。 - 返回 1。
- 返回 1。
15.2 函数定义
语法
15.2.1 静态语义：早期错误
-
如果
source text matched by FormalParameters 是strict mode code ， 则应用UniqueFormalParameters : FormalParameters -
如果存在
BindingIdentifier 并且source text matched by BindingIdentifier 是strict mode code ， 则如果StringValue 是"eval" 或"arguments" ，则为语法错误。 -
如果
FunctionBodyContainsUseStrict 为true 并且IsSimpleParameterList 为false ，则为语法错误。 -
如果
FormalParameters 的BoundNames 的任何元素也出现在LexicallyDeclaredNames 的FunctionBody 中，则为语法错误。 -
如果
FormalParameters 包含SuperProperty 为true ，则为语法错误。 -
如果
FunctionBody 包含SuperProperty 为true ，则为语法错误。 -
如果
FormalParameters 包含SuperCall 为true ，则为语法错误。 -
如果
FunctionBody 包含SuperCall 为true ，则为语法错误。
-
如果
LexicallyDeclaredNames 包含任何重复项，则为语法错误。 -
如果
LexicallyDeclaredNames 的任何元素也出现在VarDeclaredNames 的FunctionStatementList 中，则为语法错误。 -
如果
ContainsDuplicateLabels 为true ，则为语法错误。 -
如果
ContainsUndefinedBreakTarget 为true ，则为语法错误。 -
如果
ContainsUndefinedContinueTarget 为true ，则为语法错误。
15.2.2 静态语义：FunctionBodyContainsUseStrict
-
如果
Directive Prologue 的FunctionBody 包含Use Strict Directive ，则返回true ；否则，返回false 。
15.2.3 运行时语义：EvaluateFunctionBody
-
执行 ?
FunctionDeclarationInstantiation (functionObject, argumentsList)。 -
返回 ?
Evaluation 的FunctionStatementList 。
15.2.4 运行时语义：InstantiateOrdinaryFunctionObject
-
令 name 为
StringValue 的BindingIdentifier 。 -
令 sourceText 为
source text matched by 的FunctionDeclaration 。 -
令 F 为
OrdinaryFunctionCreate (%Function.prototype% ，sourceText，FormalParameters ，FunctionBody ，non-lexical-this ，env，privateEnv)。 -
执行
SetFunctionName (F，name)。 -
执行
MakeConstructor (F)。 - 返回 F。
-
令 sourceText 为
source text matched by 的FunctionDeclaration 。 -
令 F 为
OrdinaryFunctionCreate (%Function.prototype% ，sourceText，FormalParameters ，FunctionBody ，non-lexical-this ，env，privateEnv)。 -
执行
SetFunctionName (F，"default" )。 -
执行
MakeConstructor (F)。 - 返回 F。
匿名的 export default 声明的一部分出现，因此其函数代码始终是
15.2.5 运行时语义：InstantiateOrdinaryFunctionExpression
- 如果 name 不存在，则将 name 设置为空字符串。
- 令 env 为当前执行上下文的词法环境。
- 令 privateEnv 为当前执行上下文的私有环境。
-
令 sourceText 为
source text matched by 的FunctionExpression 。 -
令 closure 为
OrdinaryFunctionCreate (%Function.prototype% ，sourceText，FormalParameters ，FunctionBody ，non-lexical-this ，env，privateEnv)。 -
执行
SetFunctionName (closure，name)。 -
执行
MakeConstructor (closure)。 - 返回 closure。
-
断言 ：name 不存在。 -
设置 name 为
StringValue 的BindingIdentifier 。 - 令 outerEnv 为当前执行上下文的词法环境。
-
令 funcEnv 为
NewDeclarativeEnvironment (outerEnv)。 -
执行 ! funcEnv.CreateImmutableBinding(name,
false )。 - 令 privateEnv 为当前执行上下文的私有环境。
-
令 sourceText 为
source text matched by 的FunctionExpression 。 -
令 closure 为
OrdinaryFunctionCreate (%Function.prototype% ，sourceText，FormalParameters ，FunctionBody ，non-lexical-this ，funcEnv，privateEnv)。 -
执行
SetFunctionName (closure，name)。 -
执行
MakeConstructor (closure)。 - 执行 ! funcEnv.InitializeBinding(name, closure)。
- 返回 closure。
15.2.6 运行时语义：Evaluation
-
返回
empty 。
替代语义见
-
返回
empty 。
使用
-
返回
undefined 。
15.3 箭头函数定义
语法
补充语法
处理生产式的实例时
15.3.1 静态语义：早期错误
-
如果
ArrowParameters Contains YieldExpression 是true ，则为语法错误。 -
如果
ArrowParameters Contains AwaitExpression 是true ，则为语法错误。 -
如果
ConciseBodyContainsUseStrict 的ConciseBody 是true 并且IsSimpleParameterList 的ArrowParameters 是false ，则为语法错误。 -
如果
BoundNames 的ArrowParameters 的任何元素也出现在LexicallyDeclaredNames 的ConciseBody 中，则为语法错误。
15.3.2 静态语义：ConciseBodyContainsUseStrict
-
返回
false 。
15.3.3 运行时语义：EvaluateConciseBody
-
执行 ?
FunctionDeclarationInstantiation (functionObject，argumentsList)。 -
返回 ?
Evaluation 的ExpressionBody 。
15.3.4 运行时语义：InstantiateArrowFunctionExpression
-
如果 name 不存在，将 name 设置为
"" 。 - 令 env 为当前执行上下文的词法环境。
- 令 privateEnv 为当前执行上下文的私有环境。
-
令 sourceText 为
source text matched by 的ArrowFunction 。 -
令 closure 为
OrdinaryFunctionCreate (%Function.prototype% ，sourceText，ArrowParameters ，ConciseBody ，lexical-this ，env，privateEnv)。 -
执行
SetFunctionName (closure，name)。 - 返回 closure。
arguments，super，this 或 new.target
的本地绑定。在
arguments，super，this 或 new.target
的任何引用必须解析为词法上封闭的环境中的绑定。通常，这将是紧密封闭函数的函数环境。即使
super 的引用，在步骤
super 的
super 所需的状态可以通过
15.3.5 运行时语义：Evaluation
-
令 exprRef 为 ?
Evaluation 的AssignmentExpression 。 -
令 exprValue 为 ?
GetValue (exprRef)。 -
返回
Completion Record { [[Type]]:return ，[[Value]]：exprValue，[[Target]]：empty }。
15.4 方法定义
语法
15.4.1 静态语义：早期错误
-
如果
FunctionBodyContainsUseStrict 的FunctionBody 是true ，并且IsSimpleParameterList 的UniqueFormalParameters 是false ，则这是语法错误。 -
如果
BoundNames 的任何元素在LexicallyDeclaredNames 的FunctionBody 中也出现，则这是语法错误。
-
如果
BoundNames 的PropertySetParameterList 包含任何重复元素，则这是语法错误。 -
如果
FunctionBodyContainsUseStrict 的FunctionBody 是true ，并且IsSimpleParameterList 的PropertySetParameterList 是false ，则这是语法错误。 -
如果
BoundNames 的任何元素在LexicallyDeclaredNames 的FunctionBody 中也出现，则这是语法错误。
15.4.2 静态语义：HasDirectSuper
语法指向操作 HasDirectSuper 不接受任何参数并返回一个布尔值。它在以下生成式上逐段定义：
-
如果
UniqueFormalParameters 包含 SuperCall 是true ，则返回true 。 -
返回
FunctionBody 包含 SuperCall 。
-
返回
FunctionBody 包含 SuperCall 。
-
如果
PropertySetParameterList 包含 SuperCall 是true ，则返回true 。 -
返回
FunctionBody 包含 SuperCall 。
-
如果
UniqueFormalParameters 包含 SuperCall 是true ，则返回true 。 -
返回
GeneratorBody 包含 SuperCall 。
-
如果
UniqueFormalParameters 包含 SuperCall 是true ，则返回true 。 -
返回
AsyncGeneratorBody 包含 SuperCall 。
-
如果
UniqueFormalParameters 包含 SuperCall 是true ，则返回true 。 -
返回
AsyncFunctionBody 包含 SuperCall 。
15.4.3 静态语义：SpecialMethod
语法指向操作 SpecialMethod 不接受任何参数并返回一个布尔值。它在以下生成式上逐段定义：
- 返回
false 。
- 返回
true 。
15.4.4 运行时语义：DefineMethod
语法指向操作 DefineMethod 接受参数 object（一个对象）和可选参数 functionPrototype（一个对象），并返回一个包含字段 [[Key]]（一个属性键）和 [[Closure]]（一个 ECMAScript 函数对象）的 Record 的正常完成，或一个中断完成。它在以下生成式上逐段定义：
-
令 propKey 为 ?
Evaluation 的ClassElementName 的结果。 -
令 env 为
当前执行上下文 的 LexicalEnvironment。 -
令 privateEnv 为
当前执行上下文 的 PrivateEnvironment。 -
如果 functionPrototype 存在，则：
- 令 prototype 为 functionPrototype。
-
否则：
-
令 prototype 为
%Function.prototype% 。
-
令 prototype 为
-
令 sourceText 为
由 MethodDefinition 匹配的源文本。 -
令 closure 为
OrdinaryFunctionCreate (prototype, sourceText,UniqueFormalParameters ,FunctionBody , non-lexical-this, env, privateEnv)。 -
执行
MakeMethod (closure, object)。 - 返回 { [[Key]]: propKey, [[Closure]]: closure } 的 Record。
15.4.5 运行时语义：MethodDefinitionEvaluation
语法指向操作 MethodDefinitionEvaluation 接受参数 object（一个对象）和 enumerable（一个布尔值），并返回包含一个 PrivateElement 或 unused 的正常完成，或一个中断完成。它在以下生成式上逐段定义：
-
令 methodDef 为 ?
DefineMethod 的结果。 -
执行
SetFunctionName (methodDef.[[Closure]], methodDef.[[Key]])。 -
返回 ?
DefineMethodProperty (object, methodDef.[[Key]], methodDef.[[Closure]], enumerable)。
-
令 propKey 为 ?
Evaluation 的ClassElementName 的结果。 -
令 env 为
当前执行上下文 的 LexicalEnvironment。 -
令 privateEnv 为
当前执行上下文 的 PrivateEnvironment。 -
令 sourceText 为
由 MethodDefinition 匹配的源文本。 -
令 formalParameterList 为生产式
FormalParameters : [empty] -
令 closure 为
OrdinaryFunctionCreate (%Function.prototype% , sourceText, formalParameterList,FunctionBody , non-lexical-this, env, privateEnv)。 -
执行
MakeMethod (closure, object)。 -
执行
SetFunctionName (closure, propKey, "get")。 -
如果 propKey 是一个
私有名称 ，则：- 返回 { [[Key]]: propKey, [[Kind]]: accessor, [[Get]]: closure, [[Set]]: undefined } 的 PrivateElement。
-
否则：
- 令 desc 为 PropertyDescriptor { [[Get]]: closure, [[Enumerable]]: enumerable, [[Configurable]]: true }。
-
执行 ?
DefinePropertyOrThrow (object, propKey, desc)。 - 返回 unused。
-
令 propKey 为 ?
Evaluation 的ClassElementName 的结果。 -
令 env 为
当前执行上下文 的 LexicalEnvironment。 -
令 privateEnv 为
当前执行上下文 的 PrivateEnvironment。 -
令 sourceText 为
由 MethodDefinition 匹配的源文本。 -
令 closure 为
OrdinaryFunctionCreate (%Function.prototype% , sourceText,PropertySetParameterList ,FunctionBody , non-lexical-this, env, privateEnv)。 -
执行
MakeMethod (closure, object)。 -
执行
SetFunctionName (closure, propKey, "set")。 -
如果 propKey 是一个
私有名称 ，则：- 返回 { [[Key]]: propKey, [[Kind]]: accessor, [[Get]]: undefined, [[Set]]: closure } 的 PrivateElement。
-
否则：
- 令 desc 为 PropertyDescriptor { [[Set]]: closure, [[Enumerable]]: enumerable, [[Configurable]]: true }。
-
执行 ?
DefinePropertyOrThrow (object, propKey, desc)。 - 返回 unused。
-
令 propKey 为 ?
Evaluation 的ClassElementName 的结果。 -
令 env 为
当前执行上下文 的 LexicalEnvironment。 -
令 privateEnv 为
当前执行上下文 的 PrivateEnvironment。 -
令 sourceText 为
由 GeneratorMethod 匹配的源文本。 -
令 closure 为
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText,UniqueFormalParameters ,GeneratorBody , non-lexical-this, env, privateEnv)。 -
执行
MakeMethod (closure, object)。 -
执行
SetFunctionName (closure, propKey)。 -
令 prototype 为
OrdinaryObjectCreate (%GeneratorFunction.prototype.prototype% )。 -
执行 !
DefinePropertyOrThrow (closure, "prototype", PropertyDescriptor { [[Value]]: prototype, [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: false })。 -
返回 ?
DefineMethodProperty (object, propKey, closure, enumerable)。
-
令 propKey 为 ?
Evaluation 的ClassElementName 的结果。 -
令 env 为
当前执行上下文 的 LexicalEnvironment。 -
令 privateEnv 为
当前执行上下文 的 PrivateEnvironment。 -
令 sourceText 为
由 AsyncGeneratorMethod 匹配的源文本。 -
令 closure 为
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% , sourceText,UniqueFormalParameters ,AsyncGeneratorBody , non-lexical-this, env, privateEnv)。 -
执行
MakeMethod (closure, object)。 -
执行
SetFunctionName (closure, propKey)。 -
令 prototype 为
OrdinaryObjectCreate (%AsyncGeneratorFunction.prototype.prototype% )。 -
执行 !
DefinePropertyOrThrow (closure, "prototype", PropertyDescriptor { [[Value]]: prototype, [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: false })。 -
返回 ?
DefineMethodProperty (object, propKey, closure, enumerable)。
-
令 propKey 为 ?
Evaluation 的ClassElementName 的结果。 -
令 env 为
当前执行上下文 的 LexicalEnvironment。 -
令 privateEnv 为
当前执行上下文 的 PrivateEnvironment。 -
令 sourceText 为
由 AsyncMethod 匹配的源文本。 -
令 closure 为
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,UniqueFormalParameters ,AsyncFunctionBody , non-lexical-this, env, privateEnv)。 -
执行
MakeMethod (closure, object)。 -
执行
SetFunctionName (closure, propKey)。 -
返回 ?
DefineMethodProperty (object, propKey, closure, enumerable)。
15.5 生成器函数定义
语法
紧接在 yield 之后的语法上下文要求使用
15.5.1 静态语义：早期错误
- 如果
HasDirectSuper 的GeneratorMethod 为true ，则这是一个语法错误。 - 如果
UniqueFormalParameters Contains YieldExpression 为true ，则这是一个语法错误。 - 如果
FunctionBodyContainsUseStrict 的GeneratorBody 为true ，且IsSimpleParameterList 的UniqueFormalParameters 为false ，则这是一个语法错误。 - 如果
BoundNames 的UniqueFormalParameters 的任何元素也出现在LexicallyDeclaredNames 中，则这是一个语法错误。
- 如果
源文本匹配 的FormalParameters 是严格模式代码 ，则适用UniqueFormalParameters : FormalParameters - 如果存在
BindingIdentifier 且源文本匹配 的BindingIdentifier 是严格模式代码 ，则如果StringValue 为"eval" 或"arguments" ，则这是一个语法错误。 - 如果
FunctionBodyContainsUseStrict 的GeneratorBody 为true ，且IsSimpleParameterList 的FormalParameters 为false ，则这是一个语法错误。 - 如果
BoundNames 的FormalParameters 的任何元素也出现在LexicallyDeclaredNames 中，则这是一个语法错误。 - 如果
FormalParameters Contains YieldExpression 为true ，则这是一个语法错误。 - 如果
FormalParameters Contains SuperProperty 为true ，则这是一个语法错误。 - 如果
GeneratorBody Contains SuperProperty 为true ，则这是一个语法错误。 - 如果
FormalParameters Contains SuperCall 为true ，则这是一个语法错误。 - 如果
GeneratorBody Contains SuperCall 为true ，则这是一个语法错误。
15.5.2 运行时语义：EvaluateGeneratorBody
语法导向操作
- 执行 ?
FunctionDeclarationInstantiation (functionObject, argumentsList)。 - 令 G 为 ?
OrdinaryCreateFromConstructor (functionObject,"%GeneratorFunction.prototype.prototype%" ，« [[GeneratorState]], [[GeneratorContext]], [[GeneratorBrand]] »)。 - 将 G.[[GeneratorBrand]] 设置为
empty 。 - 执行
GeneratorStart (G,FunctionBody )。 - 返回
完成记录 { [[Type]]:return , [[Value]]: G, [[Target]]:empty }。
15.5.3 运行时语义：InstantiateGeneratorFunctionObject
语法导向操作
- 令 name 为
StringValue 的BindingIdentifier 。 - 令 sourceText 为与
GeneratorDeclaration 匹配的GeneratorDeclaration 的源文本。 - 令 F 为
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText，FormalParameters ，GeneratorBody ，non-lexical-this ，env，privateEnv）。 - 执行
SetFunctionName (F， name)。 - 令 prototype 为
OrdinaryObjectCreate (%GeneratorFunction.prototype.prototype% ). - 执行 !
DefinePropertyOrThrow (F，"prototype" ，属性描述符 { [[Value]]: prototype，[[Writable]]:true ，[[Enumerable]]:false ，[[Configurable]]:false }）。 - 返回 F。
- 令 sourceText 为与
GeneratorDeclaration 匹配的GeneratorDeclaration 的源文本。 - 令 F 为
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText，FormalParameters ，GeneratorBody ，non-lexical-this ，env，privateEnv）。 - 执行
SetFunctionName (F，"default" )。 - 令 prototype 为
OrdinaryObjectCreate (%GeneratorFunction.prototype.prototype% ). - 执行 !
DefinePropertyOrThrow (F，"prototype" ，属性描述符 { [[Value]]: prototype，[[Writable]]:true ，[[Enumerable]]:false ，[[Configurable]]:false }）。 - 返回 F。
匿名的 export default 声明的一部分出现，因此其函数代码始终是
15.5.4 运行时语义：实例化生成器函数表达式
- 如果 name 不存在，将 name 设为空字符串
"" 。 - 令 env 为当前运行执行上下文的
词法环境 。 - 令 privateEnv 为当前运行执行上下文的
私有环境 。 - 令 sourceText 为与
语法指导操作 GeneratorExpression 匹配的源文本。 - 令 closure 为
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText,FormalParameters ,GeneratorBody ,non-lexical-this , env, privateEnv)。 - 执行
SetFunctionName (closure, name)。 - 令 prototype 为
OrdinaryObjectCreate (%GeneratorFunction.prototype.prototype% )。 - 执行
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false })。 - 返回 closure。
15.5.5 运行时语义：求值
- 返回 ?
Yield (undefined )。
- 令 exprRef 为 ?
Evaluation 的AssignmentExpression 。 - 令 value 为 ?
GetValue (exprRef)。 - 返回 ?
Yield (value)。
- 令 generatorKind 为
GetGeneratorKind ()。 - 令 exprRef 为 ?
Evaluation 的AssignmentExpression 。 - 令 value 为 ?
GetValue (exprRef)。 - 令 iteratorRecord 为 ?
GetIterator (value, generatorKind)。 - 令 iterator 为 iteratorRecord.[[Iterator]]。
- 令 received 为
NormalCompletion (undefined )。 - 重复，直到:
- 如果 received 是
正常完成 ，则- 令 innerResult 为 ?
Call (iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]], « received.[[Value]] »)。 - 如果 generatorKind 是
async ，将 innerResult 设为 ?Await (innerResult)。 - 如果 innerResult
不是对象 ，抛出TypeError 异常。 - 令 done 为 ?
IteratorComplete (innerResult)。 - 如果 done 为
true ，则- 返回 ?
IteratorValue (innerResult)。
- 返回 ?
- 如果 generatorKind 是
async ，将 received 设为Completion (?AsyncGeneratorYield (?IteratorValue (innerResult)))。 - 否则，将 received 设为
Completion (GeneratorYield (innerResult))。
- 令 innerResult 为 ?
- 否则，如果 received 是
throw completion ，则- 令 throw 为 ?
GetMethod (iterator,"throw" )。 - 如果 throw 不是
undefined ，则- 令 innerResult 为 ?
Call (throw, iterator, « received.[[Value]] »)。 - 如果 generatorKind 是
async ，将 innerResult 设为 ?Await (innerResult)。 - 注意：内部迭代器的
throw方法抛出的异常会被传播。throw方法的正常完成与next类似。 - 如果 innerResult
不是对象 ，抛出TypeError 异常。 - 令 done 为 ?
IteratorComplete (innerResult)。 - 如果 done 为
true ，则- 返回 ?
IteratorValue (innerResult)。
- 返回 ?
- 如果 generatorKind 是
async ，将 received 设为Completion (AsyncGeneratorYield (?IteratorValue (innerResult)))。 - 否则，将 received 设为
Completion (GeneratorYield (innerResult))。
- 令 innerResult 为 ?
- 否则，
-
断言 ：received 是return completion 。 - 令 return 为 ?
GetMethod (iterator,"return" )。 - 如果 return 是
undefined ，则- 将 value 设为 received.[[Value]]。
- 如果 generatorKind 是
async ，则- 将 value 设为 ?
Await (value)。
- 将 value 设为 ?
- 返回
Completion Record { [[Type]]:return , [[Value]]: value, [[Target]]:empty }。
- 令 innerReturnResult 为 ?
Call (return, iterator, « received.[[Value]] »)。 - 如果 generatorKind 是
async ，将 innerReturnResult 设为 ?Await (innerReturnResult)。 - 如果 innerReturnResult
不是对象 ，抛出TypeError 异常。 - 令 done 为 ?
IteratorComplete (innerReturnResult)。 - 如果 done 为
true ，则- 将 value 设为 ?
IteratorValue (innerReturnResult)。 - 返回
Completion Record { [[Type]]:return , [[Value]]: value, [[Target]]:empty }。
- 将 value 设为 ?
- 如果 generatorKind 是
async ，将 received 设为Completion (AsyncGeneratorYield (?IteratorValue (innerReturnResult)))。 - 否则，将 received 设为
Completion (GeneratorYield (innerReturnResult))。
-
- 令 throw 为 ?
- 如果 received 是
15.6 异步生成器函数定义
语法
15.6.1 静态语义：早期错误
-
如果
HasDirectSuper ofAsyncGeneratorMethod istrue ，则这是一个语法错误。 -
如果
UniqueFormalParameters Contains YieldExpression istrue ，则这是一个语法错误。 -
如果
UniqueFormalParameters Contains AwaitExpression istrue ，则这是一个语法错误。 -
如果
FunctionBodyContainsUseStrict ofAsyncGeneratorBody istrue 并且IsSimpleParameterList ofUniqueFormalParameters isfalse ，则这是一个语法错误。 -
如果
BoundNames ofUniqueFormalParameters 中的任何元素也出现在LexicallyDeclaredNames ofAsyncGeneratorBody 中，则这是一个语法错误。
-
如果
源文本匹配 FormalParameters 是严格模式代码 ，则适用UniqueFormalParameters : FormalParameters -
如果
BindingIdentifier 存在，并且源文本匹配 BindingIdentifier 是严格模式代码 ，如果StringValue ofBindingIdentifier 是"eval" 或"arguments" ，则这是一个语法错误。 -
如果
FunctionBodyContainsUseStrict ofAsyncGeneratorBody 是true 并且IsSimpleParameterList ofFormalParameters 是false ，则这是一个语法错误。 -
如果
BoundNames ofFormalParameters 中的任何元素也出现在LexicallyDeclaredNames ofAsyncGeneratorBody 中，则这是一个语法错误。 -
如果
FormalParameters Contains YieldExpression 是true ，则这是一个语法错误。 -
如果
FormalParameters Contains AwaitExpression 是true ，则这是一个语法错误。 -
如果
FormalParameters Contains SuperProperty 是true ，则这是一个语法错误。 -
如果
AsyncGeneratorBody Contains SuperProperty 是true ，则这是一个语法错误。 -
如果
FormalParameters Contains SuperCall 是true ，则这是一个语法错误。 -
如果
AsyncGeneratorBody Contains SuperCall 是true ，则这是一个语法错误。
15.6.2 运行时语义：EvaluateAsyncGeneratorBody
- 执行 ?
FunctionDeclarationInstantiation (functionObject, argumentsList)。 - 令 generator 为 ?
OrdinaryCreateFromConstructor (functionObject,"%AsyncGeneratorFunction.prototype.prototype%" , « [[AsyncGeneratorState]], [[AsyncGeneratorContext]], [[AsyncGeneratorQueue]], [[GeneratorBrand]] »)。 - 将 generator.[[GeneratorBrand]]
设为
empty 。 - 执行
AsyncGeneratorStart (generator,FunctionBody )。 - 返回
Completion Record { [[Type]]:return , [[Value]]: generator, [[Target]]:empty }。
15.6.3 运行时语义：InstantiateAsyncGeneratorFunctionObject
- 令 name 为
StringValue ofBindingIdentifier 。 - 令 sourceText 为
源文本匹配 AsyncGeneratorDeclaration 。 - 令 F 为
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% , sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this , env, privateEnv)。 - 执行
SetFunctionName (F, name)。 - 令 prototype 为
OrdinaryObjectCreate (%AsyncGeneratorFunction.prototype.prototype% )。 - 执行 !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false })。 - 返回 F。
- 令 sourceText 为
源文本匹配 AsyncGeneratorDeclaration 。 - 令 F 为
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% , sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this , env, privateEnv)。 - 执行
SetFunctionName (F,"default" )。 - 令 prototype 为
OrdinaryObjectCreate (%AsyncGeneratorFunction.prototype.prototype% )。 - 执行 !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false })。 - 返回 F。
匿名的
export default 声明的一部分出现。
15.6.4 运行时语义：InstantiateAsyncGeneratorFunctionExpression
在
15.6.5 运行时语义：评估
15.7 类定义
语法
类定义总是
15.7.1 静态语义：早期错误
-
如果
ClassHeritage 不存在，并且以下算法返回true ，则这是一个语法错误：
-
如果
PrototypePropertyNameList 的ClassElementList 包含多个"constructor" ，则这是一个语法错误。 -
如果
PrivateBoundIdentifiers 的ClassElementList 包含任何重复项，除非该名称一次用于 getter，一次用于 setter，并且在其他条目中未使用，并且 getter 和 setter 要么都是静态的，要么都是非静态的，则这是一个语法错误。
-
如果
PropName 的MethodDefinition 不是"constructor" ，并且HasDirectSuper 的MethodDefinition 为true ，则这是一个语法错误。 -
如果
PropName 的MethodDefinition 是"constructor" ，并且SpecialMethod 的MethodDefinition 为true ，则这是一个语法错误。
-
如果
HasDirectSuper 的MethodDefinition 为true ，则这是一个语法错误。 -
如果
PropName 的MethodDefinition 是"prototype" ，则这是一个语法错误。
- 如果
PropName 的FieldDefinition 是"constructor" ，则这是一个语法错误。
- 如果
PropName 的FieldDefinition 是"prototype" 或"constructor" ，则这是一个语法错误。
- 如果
Initializer 存在，并且ContainsArguments 的Initializer 为true ，则这是一个语法错误。 - 如果
Initializer 存在，并且Initializer Contains 的SuperCall 为true ，则这是一个语法错误。
- 如果
StringValue 的PrivateIdentifier 是"#constructor" ，则这是一个语法错误。
- 如果
LexicallyDeclaredNames 的ClassStaticBlockStatementList 包含任何重复项，则这是一个语法错误。 - 如果
LexicallyDeclaredNames 的ClassStaticBlockStatementList 中的任何元素也出现在VarDeclaredNames 的ClassStaticBlockStatementList 中，则这是一个语法错误。 - 如果
ContainsDuplicateLabels 的ClassStaticBlockStatementList 参数 « » 为true ，则这是一个语法错误。 - 如果
ContainsUndefinedBreakTarget 的ClassStaticBlockStatementList 参数 « » 为true ，则这是一个语法错误。 - 如果
ContainsUndefinedContinueTarget 的ClassStaticBlockStatementList 参数 « » 和 « » 为true ，则这是一个语法错误。 - 如果
ContainsArguments 的ClassStaticBlockStatementList 为true ，则这是一个语法错误。 - 如果
ClassStaticBlockStatementList Contains 的SuperCall 为true ，则这是一个语法错误。 - 如果
ClassStaticBlockStatementList Contains 的await为true ，则这是一个语法错误。
15.7.2 静态语义：ClassElementKind
- 如果
PropName 的MethodDefinition 是"constructor" ，返回constructor-method 。 - 返回
non-constructor-method 。
- 返回
non-constructor-method 。
- 返回
non-constructor-method 。
- 返回
empty 。
15.7.3 静态语义：ConstructorMethod
- 如果
ClassElementKind 的ClassElement 是constructor-method ，返回ClassElement 。 - 返回
empty 。
- 让 head 为
ConstructorMethod 的ClassElementList 。 - 如果 head 不是
empty ，返回 head。 - 如果
ClassElementKind 的ClassElement 是constructor-method ，返回ClassElement 。 - 返回
empty 。
早期错误规则确保只有一个名为
15.7.4 静态语义：IsStatic
- 返回
false 。
- 返回
true 。
- 返回
false 。
- 返回
true 。
- 返回
true 。
- 返回
false 。
15.7.5 静态语义：NonConstructorElements
- 如果
ClassElementKind 属于ClassElement 且为non-constructor-method ，则- 返回«
ClassElement »。
- 返回«
- 返回一个新的空
列表 。
- 让list等于
NonConstructorElements 属于ClassElementList 。 - 如果
ClassElementKind 属于ClassElement 且为non-constructor-method ，则- 将
ClassElement 追加到list的末尾。
- 将
- 返回list。
15.7.6 静态语义：PrototypePropertyNameList
- 令 propName 等于
PropName 属于ClassElement 。 - 如果 propName
是
empty ，则返回一个新的空列表 。 - 如果
IsStatic 属于ClassElement 是true ，则返回一个新的空列表 。 - 返回 « propName »。
- 令 list 等于
PrototypePropertyNameList 属于ClassElementList 。 - 令 propName 等于
PropName 属于ClassElement 。 - 如果 propName 是
empty ，则返回 list。 - 如果
IsStatic 属于ClassElement 是true ，则返回 list。 - 返回
列表连接 list 和 « propName »。
15.7.7 静态语义：AllPrivateIdentifiersValid
本规范中未列出的每个语法生成式替代项隐含有以下默认的 AllPrivateIdentifiersValid 定义：
- 对于此
解析节点 的每个子节点child，执行以下操作：- 如果 child 是一个非终结符的实例，那么
- 如果
AllPrivateIdentifiersValid 属于 child 并带有参数 names 为false ，则返回false 。
- 如果
- 如果 child 是一个非终结符的实例，那么
- 返回
true 。
- 如果 names 包含
StringValue 属于PrivateIdentifier ，那么- 返回
AllPrivateIdentifiersValid 属于MemberExpression 并带有参数 names。
- 返回
- 返回
false 。
- 如果 names 包含
StringValue 属于PrivateIdentifier ，那么- 返回
AllPrivateIdentifiersValid 属于CallExpression 并带有参数 names。
- 返回
- 返回
false 。
- 如果 names 包含
StringValue 属于PrivateIdentifier ，返回true 。 - 返回
false 。
- 如果 names 包含
StringValue 属于PrivateIdentifier ，那么- 返回
AllPrivateIdentifiersValid 属于OptionalChain 并带有参数 names。
- 返回
- 返回
false 。
- 令 newNames 等于
列表连接 names 和PrivateBoundIdentifiers 属于ClassBody 。 - 返回
AllPrivateIdentifiersValid 属于ClassElementList 并带有参数 newNames。
- 如果 names 包含
StringValue 属于PrivateIdentifier ，那么- 返回
AllPrivateIdentifiersValid 属于ShiftExpression 并带有参数 names。
- 返回
- 返回
false 。
15.7.8 静态语义：PrivateBoundIdentifiers
- 返回一个
列表 ，其唯一元素是StringValue 属于PrivateIdentifier 。
- 返回一个新的空
列表 。
- 令 names1 为
PrivateBoundIdentifiers 属于ClassElementList 。 - 令 names2 为
PrivateBoundIdentifiers 属于ClassElement 。 - 返回 names1 和 names2 的
列表连接 。
15.7.9 静态语义：ContainsArguments
本规范中未列出的每个语法生成式替代方案隐式具有以下 ContainsArguments 的默认定义：
- 对于此
解析节点 的每个子节点child，执行以下操作- 如果child是一个非终结符实例，则
- 如果
ContainsArguments 属于child为true ，则返回true 。
- 如果
- 如果child是一个非终结符实例，则
- 返回
false 。
- 如果
StringValue 属于Identifier 为"arguments" ，则返回true 。 - 返回
false 。
- 返回
false 。
- 返回
false 。
15.7.10 运行时语义: ClassFieldDefinitionEvaluation
-
令 name 为 ?
Evaluation ClassElementName 。 -
如果
Initializer 存在，那么：-
令 formalParameterList 为
FormalParameters : [empty] -
令 env 为
运行执行上下文 的词法环境。 -
令 privateEnv 为
运行执行上下文 的私有环境。 - 令 sourceText 为 Unicode 代码点的空序列。
-
令 initializer 为
OrdinaryFunctionCreate (%Function.prototype% , sourceText, formalParameterList,Initializer ,non-lexical-this , env, privateEnv)。 -
执行
MakeMethod (initializer, homeObject)。 - 设置 initializer.[[ClassFieldInitializerName]] 为 name。
-
令 formalParameterList 为
-
否则：
-
令 initializer 为
empty 。
-
令 initializer 为
-
返回
ClassFieldDefinition Record { [[Name]]: name, [[Initializer]]: initializer }。
15.7.11 运行时语义：ClassStaticBlockDefinitionEvaluation
-
令 lex 为
运行执行上下文 的词法环境。 -
令 privateEnv 为
运行执行上下文 的私有环境。 - 令 sourceText 为 Unicode 代码点的空序列。
-
令 formalParameters 为
FormalParameters : [empty] -
令 bodyFunction 为
OrdinaryFunctionCreate (%Function.prototype% , sourceText, formalParameters,ClassStaticBlockBody ,non-lexical-this , lex, privateEnv)。 -
执行
MakeMethod (bodyFunction, homeObject)。 -
返回
ClassStaticBlockDefinition Record { [[BodyFunction]]: bodyFunction }。
15.7.12 运行时语义：EvaluateClassStaticBlockBody
-
断言 ：functionObject 是由ClassStaticBlockDefinitionEvaluation 第5 步创建的合成函数。 -
执行 !
FunctionDeclarationInstantiation (functionObject, « »)。 -
返回 ?
Evaluation ofClassStaticBlockStatementList 。
15.7.13 运行时语义：ClassElementEvaluation
- 返回 ?
ClassFieldDefinitionEvaluation 的FieldDefinition 参数为 object。
- 返回 ?
MethodDefinitionEvaluation 的MethodDefinition 参数为 object 和false 。
- 返回
ClassStaticBlockDefinitionEvaluation 的ClassStaticBlock 参数为 object。
- 返回
unused 。
15.7.14 运行时语义：ClassDefinitionEvaluation
为了方便规范，私有方法和访问器与私有字段一起包含在类实例的 [[PrivateElements]] 插槽中。然而，任何给定对象都具有某个类定义的所有或无任何私有方法和访问器。此功能的设计使得实现可以选择使用不需要单独跟踪每个方法或访问器的策略来实现私有方法和访问器。
例如，实现可以直接将实例私有方法与相应的 this 值运行。然后在对象上查找实例私有方法的过程是检查定义该方法的类
这与私有字段不同：因为字段初始化程序在类实例化期间可能会抛出异常，个别对象可能具有给定类的某些私有字段的子集，因此一般需要单独跟踪私有字段。
其分段定义如下生产：
- 令 env 为
运行执行上下文 的 LexicalEnvironment。 - 令 classEnv 为
NewDeclarativeEnvironment (env)。 - 如果 classBinding 不是
undefined ，则- 执行
! classEnv.CreateImmutableBinding(classBinding,
true )。
- 执行
! classEnv.CreateImmutableBinding(classBinding,
- 令 outerPrivateEnvironment 为
运行执行上下文 的 PrivateEnvironment。 - 令 classPrivateEnvironment 为
NewPrivateEnvironment (outerPrivateEnvironment)。 - 如果
ClassBody 存在，则- 对于
PrivateBoundIdentifiers 的每个字符串 dn，都
- 对于
- 如果
ClassHeritage 不存在，则- 令 protoParent 为
%Object.prototype% 。 - 令 constructorParent 为
%Function.prototype% 。
- 令 protoParent 为
- 否则，
- 将
运行执行上下文 的 LexicalEnvironment 设置为 classEnv。 - 注意：在评估
ClassHeritage 时，运行执行上下文 的 PrivateEnvironment 是 outerPrivateEnvironment。 - 令 superclassRef 为
Completion (Evaluation 的ClassHeritage )。 - 将
运行执行上下文 的 LexicalEnvironment 设置为 env。 - 令 superclass 为 ?
GetValue (? superclassRef)。 - 如果 superclass 是
null ，则- 令 protoParent 为
null 。 - 令 constructorParent 为
%Function.prototype% 。
- 令 protoParent 为
- 否则如果
IsConstructor (superclass) 是false ，则- 抛出一个
TypeError 异常。
- 抛出一个
- 否则，
- 将
- 令 proto 为
OrdinaryObjectCreate (protoParent)。 - 如果
ClassBody 不存在，令 constructor 为empty 。 - 否则，令 constructor 为
ConstructorMethod 的ClassBody 。 - 将
运行执行上下文 的 LexicalEnvironment 设置为 classEnv。 - 将
运行执行上下文 的 PrivateEnvironment 设置为 classPrivateEnvironment。 - 如果 constructor 是
empty ，则- 令 defaultConstructor 为一个新的
抽象闭包 ，它没有参数且不捕获任何内容，当被调用时执行以下步骤：- 令 args 为传递给此函数的由 [[Call]] 或 [[Construct]] 传递的参数列表。
- 如果 NewTarget 是
undefined ，则抛出一个TypeError 异常。 - 令 F 为
活动函数对象 。 - 如果 F.[[ConstructorKind]] 是
derived ，则- 注意：此分支的行为类似于
constructor(...args) { super(...args); }。最显著的区别在于，虽然前述的ECMAScript 源代码 可观察到调用%Array.prototype%上的@@iterator 方法，但此函数不会。 - 令 func 为 ! F.[[GetPrototypeOf]]()。
- 如果
IsConstructor (func) 是false ，则抛出一个TypeError 异常。 - 令 result 为 ?
Construct (func, args, NewTarget)。
- 注意：此分支的行为类似于
- 否则，
- 注意：此分支的行为类似于
constructor() {}。 - 令 result 为 ?
OrdinaryCreateFromConstructor (NewTarget,"%Object.prototype%" )。
- 注意：此分支的行为类似于
- 执行 ?
InitializeInstanceElements (result, F)。 - 返回 result。
- 令 F 为
CreateBuiltinFunction (defaultConstructor, 0, className, « [[ConstructorKind]], [[SourceText]] »,当前 Realm 记录 , constructorParent)。
- 令 defaultConstructor 为一个新的
- 否则，
- 令 constructorInfo 为 !
DefineMethod (constructor，带参数 proto 和 constructorParent)。 - 令 F 为 constructorInfo.[[Closure]]。
- 执行
MakeClassConstructor (F)。 - 执行
SetFunctionName (F, className)。
- 令 constructorInfo 为 !
- 执行
MakeConstructor (F,false , proto)。 - 如果
ClassHeritage 存在，设置 F.[[ConstructorKind]] 为derived 。 - 执行 !
DefineMethodProperty (proto,"constructor" , F,false )。 - 如果
ClassBody 不存在，令 elements 为一个新的空的列表 。 - 否则，令 elements 为
NonConstructorElements 的ClassBody 。 - 令 instancePrivateMethods 为一个新的空的
列表 。 - 令 staticPrivateMethods 为一个新的空的
列表 。 - 令 instanceFields 为一个新的空的
列表 。 - 令 staticElements 为一个新的空的
列表 。 - 对于 elements 的每个
ClassElement e，执行- 如果
IsStatic 的 e 是false ，则- 令 element 为
Completion (ClassElementEvaluation 的 e 带参数 proto)。
- 令 element 为
- 否则，
- 令 element 为
Completion (ClassElementEvaluation 的 e 带参数 F)。
- 令 element 为
- 如果 element 是一个
中止完成 ，则 - 设置 element 为 ! element。
- 如果 element 是一个
PrivateElement ，则断言 ：element.[[Kind]] 不是method 或accessor 。- 如果
IsStatic 的 e 是false ，令 container 为 instancePrivateMethods。 - 否则，令 container 为 staticPrivateMethods。
- 如果 container 包含一个
PrivateElement pe，且 pe.[[Key]] 是 element.[[Key]]，则断言 ：element.[[Kind]] 和 pe.[[Kind]] 均为accessor 。- 如果 element.[[Get]]
是
undefined ，则- 令 combined 为
PrivateElement { [[Key]]: element.[[Key]], [[Kind]]:accessor , [[Get]]: pe.[[Get]], [[Set]]: element.[[Set]] }。
- 令 combined 为
- 否则，
- 令 combined 为
PrivateElement { [[Key]]: element.[[Key]], [[Kind]]:accessor , [[Get]]: element.[[Get]], [[Set]]: pe.[[Set]] }。
- 令 combined 为
- 用 combined 替换 container 中的 pe。
- 否则，
- 将 element 添加到 container。
- 否则如果 element 是一个
ClassFieldDefinition 记录 ，则- 如果
IsStatic 的 e 是false ，将 element 添加到 instanceFields。 - 否则，将 element 添加到 staticElements。
- 如果
- 否则如果 element 是一个
ClassStaticBlockDefinition 记录 ，则- 将 element 添加到 staticElements。
- 如果
- 将
运行执行上下文 的 LexicalEnvironment 设置为 env。 - 如果 classBinding 不是
undefined ，则- 执行 ! classEnv.InitializeBinding(classBinding, F)。
- 设置 F.[[PrivateMethods]] 为 instancePrivateMethods。
- 设置 F.[[Fields]] 为 instanceFields。
- 对于 staticPrivateMethods 的每个
PrivateElement method，执行- 执行 !
PrivateMethodOrAccessorAdd (F, method)。
- 执行 !
- 对于 staticElements 的每个 elementRecord，执行
- 如果 elementRecord 是一个
ClassFieldDefinition 记录 ，则- 令 result 为
Completion (DefineField (F, elementRecord))。
- 令 result 为
- 否则，
断言 ：elementRecord 是一个ClassStaticBlockDefinition 记录 。- 令 result 为
Completion (Call (elementRecord.[[BodyFunction]], F))。
- 如果 result 是一个
中止完成 ，则- 将
运行执行上下文 的 PrivateEnvironment 设置为 outerPrivateEnvironment。 - 返回 ? result。
- 将
- 如果 elementRecord 是一个
- 将
运行执行上下文 的 PrivateEnvironment 设置为 outerPrivateEnvironment。 - 返回 F。
15.7.15 Runtime语义: BindingClassDeclarationEvaluation
- 让 className 为
StringValue ofBindingIdentifier 。 - 让 value 为 ?
ClassDefinitionEvaluation ofClassTail with arguments className 和 className。 - 将 value.[[SourceText]] 设置为
由 ClassDeclaration 匹配的源代码文本。 - 让 env 为
运行执行上下文 的词法环境。 - 执行 ?
InitializeBoundName (className, value, env)。 - 返回 value。
- 让 value 为 ?
ClassDefinitionEvaluation ofClassTail with argumentsundefined 和"default" 。 - 将 value.[[SourceText]] 设置为
由 ClassDeclaration 匹配的源代码文本。 - 返回 value。
15.7.16 Runtime语义: Evaluation
- 执行 ?
BindingClassDeclarationEvaluation of thisClassDeclaration 。 - 返回
empty 。
- 让 value 为 ?
ClassDefinitionEvaluation ofClassTail with argumentsundefined 和"" 。 - 将 value.[[SourceText]] 设置为
由 ClassExpression 匹配的源代码文本。 - 返回 value。
- 让 className 为
StringValue ofBindingIdentifier 。 - 让 value 为 ?
ClassDefinitionEvaluation ofClassTail with arguments className 和 className。 - 将 value.[[SourceText]] 设置为
由 ClassExpression 匹配的源代码文本。 - 返回 value。
- 让 privateIdentifier 为
StringValue ofPrivateIdentifier 。 - 让 privateEnvRec 为
running execution context 的 PrivateEnvironment。 - 让 names 为 privateEnvRec.[[Names]]。
-
断言 : names 中正好有一个元素是Private Name ，其 [[Description]] 为 privateIdentifier。 - 让 privateName 为
Private Name 中的 names，其 [[Description]] 为 privateIdentifier。 - 返回 privateName。
- 返回
undefined 。
15.8 异步函数定义
语法
当 [Await] 参数存在时，await 作为
- 在
AsyncFunctionBody 中。 - 在
FormalParameters 中，例如AsyncFunctionDeclaration ，AsyncFunctionExpression ，AsyncGeneratorDeclaration ，或AsyncGeneratorExpression 。在这种位置上的AwaitExpression 通过静态语义 是语法错误。 - 在
模块 中。
不同于
15.8.1 静态语义：早期错误
-
如果
FunctionBodyContainsUseStrict 为AsyncFunctionBody 为true 且IsSimpleParameterList 的UniqueFormalParameters 为false ，则这是语法错误。 -
如果
HasDirectSuper 的AsyncMethod 为true ，则这是语法错误。 -
如果
UniqueFormalParameters Contains AwaitExpression 为true ，则这是语法错误。 -
如果
BoundNames 的任何元素UniqueFormalParameters 也出现在LexicallyDeclaredNames 的AsyncFunctionBody 中，则这是语法错误。
-
如果
FunctionBodyContainsUseStrict 的AsyncFunctionBody 是true 且IsSimpleParameterList 的FormalParameters 是false ，则这是语法错误。 -
如果
FormalParameters Contains AwaitExpression 是true ，则这是语法错误。 -
如果
源文本匹配 的FormalParameters 是严格模式代码 ，则应用UniqueFormalParameters : FormalParameters -
如果
BindingIdentifier 存在且源文本匹配 的BindingIdentifier 是严格模式代码 ，则如果StringValue 的BindingIdentifier 为"eval" 或"arguments" ，则这是语法错误。 -
如果
BoundNames 的任何元素FormalParameters 也出现在LexicallyDeclaredNames 的AsyncFunctionBody 中，则这是语法错误。 -
如果
FormalParameters Contains SuperProperty 是true ，则这是语法错误。 -
如果
AsyncFunctionBody Contains SuperProperty 是true ，则这是语法错误。 -
如果
FormalParameters Contains SuperCall 是true ，则这是语法错误。 -
如果
AsyncFunctionBody Contains SuperCall 是true ，则这是语法错误。
15.8.2 运行时语义：实例化异步函数对象
- 令 name 为
StringValue 的BindingIdentifier 。 - 令 sourceText 为
源文本匹配 的AsyncFunctionDeclaration 。 - 令 F 为
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this , env, privateEnv)。 - 执行
SetFunctionName (F, name)。 - 返回 F。
- 令 sourceText 为
源文本匹配 的AsyncFunctionDeclaration 。 - 令 F 为
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this , env, privateEnv)。 - 执行
SetFunctionName (F,"default" )。 - 返回 F。
15.8.3 运行时语义：实例化异步函数表达式
- 如果 name 不存在，则将 name 设置为
"" 。 - 令 env 为
当前执行上下文 的 LexicalEnvironment。 - 令 privateEnv 为
当前执行上下文 的 PrivateEnvironment。 - 令 sourceText 为
源文本匹配 的AsyncFunctionExpression 。 - 令 closure 为
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this , env, privateEnv)。 - 执行
SetFunctionName (closure, name)。 - 返回 closure。
-
断言 ：name 不存在。 - 将 name 设置为
StringValue 的BindingIdentifier 。 - 令 outerEnv 为
当前执行上下文 的 LexicalEnvironment。 - 令 funcEnv 为
NewDeclarativeEnvironment (outerEnv)。 - 执行
! funcEnv.CreateImmutableBinding(name,
false )。 - 令 privateEnv 为
当前执行上下文 的 PrivateEnvironment。 - 令 sourceText 为
源文本匹配 的AsyncFunctionExpression 。 - 令 closure 为
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this , funcEnv, privateEnv)。 - 执行
SetFunctionName (closure, name)。 - 执行 ! funcEnv.InitializeBinding(name, closure)。
- 返回 closure。
15.8.4 运行时语义：评估异步函数体
- 令 promiseCapability 为 !
NewPromiseCapability (%Promise% )。 - 令 declResult 为
Completion (FunctionDeclarationInstantiation (functionObject, argumentsList))。 - 如果 declResult 是
突然完成 ，则- 执行 !
Call (promiseCapability.[[Reject]],undefined , «declResult.[[Value]]»)。
- 执行 !
- 否则，
- 执行
AsyncFunctionStart (promiseCapability,FunctionBody )。
- 执行
- 返回
完成记录 { [[Type]]:return , [[Value]]: promiseCapability.[[Promise]], [[Target]]:empty }。
15.8.5 运行时语义：评估
- 令 exprRef 为 ?
Evaluation 的UnaryExpression 。 - 令 value 为 ?
GetValue (exprRef)。 - 返回 ?
Await (value)。
15.9 Async Arrow Function 定义
语法
补充语法
当处理以下生成式的一个实例时
对
15.9.1 静态语义：早期错误
- 如果
BoundNames 中的任何元素在AsyncArrowBindingIdentifier 中出现并且在LexicallyDeclaredNames 的AsyncConciseBody 中也出现，则这是语法错误。
-
CoverCallExpressionAndAsyncArrowHead 必须覆盖 一个AsyncArrowHead 。 - 如果
CoverCallExpressionAndAsyncArrowHead 包含 YieldExpression 是true ，则这是语法错误。 - 如果
CoverCallExpressionAndAsyncArrowHead 包含 AwaitExpression 是true ，则这是语法错误。 - 如果
BoundNames 中的任何元素在CoverCallExpressionAndAsyncArrowHead 中出现并且在LexicallyDeclaredNames 的AsyncConciseBody 中也出现，则这是语法错误。 - 如果
AsyncConciseBodyContainsUseStrict 的AsyncConciseBody 是true 并且IsSimpleParameterList 的CoverCallExpressionAndAsyncArrowHead 是false ，则这是语法错误。
15.9.2 静态语义：AsyncConciseBodyContainsUseStrict
-
返回
false 。
15.9.3 运行时语义：EvaluateAsyncConciseBody
-
让 promiseCapability 为 !
NewPromiseCapability (%Promise% )。 -
让 declResult 为
Completion (FunctionDeclarationInstantiation (functionObject, argumentsList))。 -
如果 declResult 是一个
突然完成 ，则-
执行 !
Call (promiseCapability.[[Reject]]，undefined ，« declResult.[[Value]] »）。
-
执行 !
-
否则，
-
执行
AsyncFunctionStart (promiseCapability，ExpressionBody )。
-
执行
-
返回
完成记录 { [[Type]]:return ，[[Value]]: promiseCapability.[[Promise]]，[[Target]]:empty }。
15.9.4 运行时语义：InstantiateAsyncArrowFunctionExpression
-
如果 name 不存在，将 name 设置为
"" 。 -
让 env 为
运行执行上下文 的 LexicalEnvironment。 -
让 privateEnv 为
运行执行上下文 的 PrivateEnvironment。 -
让 sourceText 为
匹配的源文本 AsyncArrowFunction 。 -
让 parameters 为
AsyncArrowBindingIdentifier 。 -
让 closure 为
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText, parameters,AsyncConciseBody ,lexical-this , env, privateEnv)。 -
执行
SetFunctionName (closure, name)。 - 返回 closure。
-
如果 name 不存在，将 name 设置为
"" 。 -
让 env 为
运行执行上下文 的 LexicalEnvironment。 -
让 privateEnv 为
运行执行上下文 的 PrivateEnvironment。 -
让 sourceText 为
匹配的源文本 AsyncArrowFunction 。 -
让 head 为
AsyncArrowHead 是覆盖的 CoverCallExpressionAndAsyncArrowHead 。 -
让 parameters 为
ArrowFormalParameters 的 head。 -
让 closure 为
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText, parameters,AsyncConciseBody ,lexical-this , env, privateEnv)。 -
执行
SetFunctionName (closure, name)。 - 返回 closure。
15.9.5 运行时语义：评估
15.10 尾调用
15.10.1 静态语义：IsInTailPosition ( call )
抽象操作 IsInTailPosition 接受参数 call（一个
- 如果
源文本匹配 call 是非严格模式代码 ，返回false 。 - 如果 call 不包含在
FunctionBody 、ConciseBody 或AsyncConciseBody 中，返回false 。 - 让 body 为最紧密包含 call 的
FunctionBody 、ConciseBody 或AsyncConciseBody 。 - 如果 body 是
FunctionBody 的GeneratorBody ，返回false 。 - 如果 body 是
FunctionBody 的AsyncFunctionBody ，返回false 。 - 如果 body 是
FunctionBody 的AsyncGeneratorBody ，返回false 。 - 如果 body 是
AsyncConciseBody ，返回false 。 - 返回
HasCallInTailPosition 在 body 上的结果，参数为 call。
15.10.2 静态语义：HasCallInTailPosition
它的定义依赖于以下几种产生式：
- 令 has 为
HasCallInTailPosition 对于StatementList 的结果，参数为 call。 - 如果 has 为
true ，则返回true 。 - 返回
HasCallInTailPosition 对于StatementListItem 的结果，参数为 call。
- 返回
false 。
- 让 has 为第一个
Statement 的HasCallInTailPosition 的结果，参数为 call。 - 如果 has 为
true ，返回true 。 - 返回第二个
Statement 的HasCallInTailPosition 的结果，参数为 call。
- 返回第一个
Statement 的HasCallInTailPosition 的结果，参数为 call。
- 返回第一个
LabelledItem 的HasCallInTailPosition 的结果，参数为 call。
- 返回第一个
Expression 的HasCallInTailPosition 的结果，参数为 call。
- 返回
HasCallInTailPosition 对CaseBlock 的结果，参数为 call。
- 让 has 为
false 。 - 如果存在第一个
CaseClauses ，则将 has 设为HasCallInTailPosition 对第一个CaseClauses 的结果，参数为 call。 - 如果 has 为
true ，则返回true 。 - 将 has 设为
HasCallInTailPosition 对DefaultClause 的结果，参数为 call。 - 如果 has 为
true ，则返回true 。 - 如果存在第二个
CaseClauses ，则将 has 设为HasCallInTailPosition 对第二个CaseClauses 的结果，参数为 call。 - 返回 has。
- 让 has 为
HasCallInTailPosition 对CaseClauses 的结果，参数为 call。 - 如果 has 为
true ，则返回true 。 - 返回
HasCallInTailPosition 对CaseClause 的结果，参数为 call。
- 如果存在
StatementList ，则返回HasCallInTailPosition 对StatementList 的结果，参数为 call。 - 返回
false 。
- 返回
HasCallInTailPosition 对Catch 的结果，参数为 call。
- 返回
HasCallInTailPosition 对Finally 的结果，参数为 call。
- 返回
HasCallInTailPosition 对Block 的结果，参数为 call。
- 返回
false 。
- 返回
HasCallInTailPosition 对AssignmentExpression 的调用，参数为 call。
- 让 has 为第一个
AssignmentExpression 的HasCallInTailPosition 调用，参数为 call。 - 如果 has 为
true ，返回true 。 - 返回第二个
AssignmentExpression 的HasCallInTailPosition 调用，参数为 call。
- 返回
HasCallInTailPosition 对BitwiseORExpression 的 调用，参数为 call。
- 返回
HasCallInTailPosition 对LogicalANDExpression 的 调用，参数为 call。
- 返回
HasCallInTailPosition 对BitwiseORExpression 的 调用，参数为 call。
- 如果此
CallExpression 是 call，则返回true 。 - 返回
false 。
- 返回
HasCallInTailPosition 对OptionalChain 的结果，参数为 call。
- 返回
false 。
- 如果这个
OptionalChain 是 call，则返回true 。 - 返回
false 。
- 如果这个
MemberExpression 是 call，则返回true 。 - 返回
false 。
- 令 expr 为由
ParenthesizedExpression 表示的表达式，该表达式由覆盖 ，由CoverParenthesizedExpressionAndArrowParameterList 包含。 - 返回
HasCallInTailPosition 对 expr 和参数 call 的结果。
- 返回
HasCallInTailPosition 对Expression 和参数 call 的结果。
15.10.3 PrepareForTailCall ( )
抽象操作 PrepareForTailCall 不接受任何参数，并返回
尾位置调用必须在调用目标函数之前释放当前执行函数的任何瞬态内部资源
例如，尾位置调用应该仅在目标函数的激活记录的大小超出调用函数的激活记录大小时，才增加实现的激活记录栈的大小。如果目标函数的激活记录更小，则栈的总大小应减少。
16 ECMAScript 语言：脚本和模块
16.1 脚本
语法
16.1.1 静态语义：早期错误
-
如果
LexicallyDeclaredNames 中包含任何重复条目，则会导致语法错误。 -
如果
LexicallyDeclaredNames 中的任何元素也出现在VarDeclaredNames 中，则会导致语法错误。
-
如果
StatementList Contains super，除非包含super的源文本是由直接 eval 处理的 eval 代码。有关super在直接 eval 中的附加早期错误规则，请参见19.2.1.1 。 -
如果
StatementList Contains NewTarget ，除非包含NewTarget 的源文本是由直接 eval 处理的 eval 代码。有关NewTarget 在直接 eval 中的附加早期错误规则，请参见19.2.1.1 。 -
如果
ContainsDuplicateLabels 的StatementList 的结果为true ，则会导致语法错误。 -
如果
ContainsUndefinedBreakTarget 的StatementList 的结果为true ，则会导致语法错误。 -
如果
ContainsUndefinedContinueTarget 的StatementList 的结果为true ，则会导致语法错误。 -
如果
AllPrivateIdentifiersValid 的StatementList 的结果为false ，除非包含ScriptBody 的源文本是由直接 eval 处理的 eval 代码。
16.1.2 静态语义：IsStrict
语法导向操作
- 如果
ScriptBody 存在且Directive Prologue 中包含Use Strict Directive ，则返回true ；否则，返回false 。
16.1.3 运行时语义：评估
- 返回
undefined 。
16.1.4 脚本记录
脚本记录 封装了有关正在评估的脚本的信息。每个脚本记录包含了
| 字段名称 | 值类型 | 含义 |
|---|---|---|
| [[Realm]] | 一个 |
此脚本创建时所在的 |
| [[ECMAScriptCode]] | 一个 |
解析此脚本的源文本后的结果。 |
| [[LoadedModules]] | 一个 |
从此脚本导入的规范符字符串到解析的 |
| [[HostDefined]] | 任何东西（默认值为 |
供 |
16.1.5 解析脚本 ( sourceText, realm, hostDefined )
抽象操作 ParseScript 接受以下参数：sourceText（
实现可以在对脚本源文本进行 ParseScript 之前解析脚本源文本并分析其早期错误条件。然而，任何错误的报告必须推迟到本规范实际对该源文本执行 ParseScript 的时候。
16.1.6 脚本评估 ( scriptRecord )
抽象操作 ScriptEvaluation 接受一个参数 scriptRecord（一个
- 将 globalEnv 设为 scriptRecord.[[Realm]].[[GlobalEnv]]。
- 将 scriptContext 设为一个新的
ECMAScript 代码执行上下文 。 - 将 scriptContext 的 Function 设为
null 。 - 将
Realm 设为 scriptContext 的 [[Realm]]。 - 将 scriptContext 的 ScriptOrModule 设为 scriptRecord。
- 将 scriptContext 的 VariableEnvironment 设为 globalEnv。
- 将 scriptContext 的 LexicalEnvironment 设为 globalEnv。
- 将 scriptContext 的 PrivateEnvironment 设为
null 。 - 挂起
运行中的执行上下文 。 - 将 scriptContext 推送到
执行上下文栈 ；此时 scriptContext 是运行中的执行上下文 。 - 将 script 设为 scriptRecord.[[ECMAScriptCode]]。
- 将 result 设为
Completion (GlobalDeclarationInstantiation (script, globalEnv))。 - 如果 result 是一个
正常完成 ，则- 将 result 设为
Completion (Evaluation of script)。 - 如果 result 是一个
正常完成 且 result.[[Value]] 是empty ，则- 将 result 设为
NormalCompletion (undefined )。
- 将 result 设为
- 将 result 设为
- 挂起 scriptContext 并将其从
执行上下文栈 中移除。 Assert :执行上下文栈 不能为空。- 恢复当前在
执行上下文栈 顶部的上下文作为运行中的执行上下文 。 - 返回 ? result。
16.1.7 GlobalDeclarationInstantiation ( script, env )
抽象操作 GlobalDeclarationInstantiation 接受两个参数：script（一个
在为脚本评估建立执行上下文时，声明会在当前全局环境中被实例化。代码中声明的每个全局绑定都会被实例化。
调用时执行以下步骤：
- 令 lexNames 为
LexicallyDeclaredNames 的 script。 - 令 varNames 为
VarDeclaredNames 的 script。 - 对 lexNames 的每个元素 name 执行
- 如果 env.HasVarDeclaration(name) 为
true ，抛出SyntaxError 异常。 - 如果 env.HasLexicalDeclaration(name) 为
true ，抛出SyntaxError 异常。 - 令 hasRestrictedGlobal 为 ? env.HasRestrictedGlobalProperty(name)。
- 如果 hasRestrictedGlobal 为
true ，抛出SyntaxError 异常。
- 如果 env.HasVarDeclaration(name) 为
- 对 varNames 的每个元素 name 执行
- 如果 env.HasLexicalDeclaration(name) 为
true ，抛出SyntaxError 异常。
- 如果 env.HasLexicalDeclaration(name) 为
- 令 varDeclarations 为
VarScopedDeclarations 的 script。 - 令 functionsToInitialize 为一个新的空的
List 。 - 令 declaredFunctionNames 为一个新的空的
List 。 - 对 varDeclarations 的每个元素 d（按逆序
List 顺序）执行- 如果 d 既不是
VariableDeclaration ，也不是ForBinding ，或BindingIdentifier ，则Assert ：d 是一个FunctionDeclaration 、GeneratorDeclaration 、AsyncFunctionDeclaration ，或AsyncGeneratorDeclaration 。- 注意：如果有多个相同名称的函数声明，则使用最后一个声明。
- 令 fn 为 d 的唯一元素的
BoundNames 。 - 如果 declaredFunctionNames 中不包含 fn，则
- 令 fnDefinable 为 ? env.CanDeclareGlobalFunction(fn)。
- 如果 fnDefinable 为
false ，抛出TypeError 异常。 - 将 fn 添加到 declaredFunctionNames 中。
- 将 d 作为第一个元素插入到 functionsToInitialize 中。
- 如果 d 既不是
- 令 declaredVarNames 为一个新的空的
List 。 - 对 varDeclarations 的每个元素 d 执行
- 如果 d 是
VariableDeclaration 、ForBinding ，或BindingIdentifier ，则- 对 d 的
BoundNames 的每个字符串 vn 执行- 如果 declaredFunctionNames 中不包含
vn，则
- 令 vnDefinable 为 ? env.CanDeclareGlobalVar(vn)。
- 如果 vnDefinable 为
false ，抛出TypeError 异常。 - 如果 declaredVarNames 中不包含 vn，则
- 将 vn 添加到 declaredVarNames 中。
- 如果 declaredFunctionNames 中不包含
vn，则
- 对 d 的
- 如果 d 是
- 注意：如果
global object 是一个ordinary object ，则此算法步骤不会发生异常终止。然而，如果global object 是一个Proxy exotic object ，它可能表现出导致后续步骤异常终止的行为。 - 注意：附录
B.3.2.2 在此处添加了额外的步骤。 - 令 lexDeclarations 为
LexicallyScopedDeclarations 的 script。 - 令 privateEnv 为
null 。 - 对 lexDeclarations 的每个元素 d 执行
- 注意：词法声明的名称仅在此处实例化，但不会初始化。
- 对 d 的
BoundNames 的每个元素 dn 执行- 如果
IsConstantDeclaration 为true ，则- 执行 ? env.CreateImmutableBinding(dn,
true )。
- 执行 ? env.CreateImmutableBinding(dn,
- 否则，
- 执行 ? env.CreateMutableBinding(dn,
false )。
- 执行 ? env.CreateMutableBinding(dn,
- 如果
- 对 functionsToInitialize 的每个
Parse Node f 执行- 令 fn 为 f 的唯一元素的
BoundNames 。 - 令 fo 为
InstantiateFunctionObject 的 f，参数为 env 和 privateEnv。 - 执行 ? env.CreateGlobalFunctionBinding(fn,
fo,
false )。
- 令 fn 为 f 的唯一元素的
- 对 declaredVarNames 的每个字符串 vn 执行
- 执行 ? env.CreateGlobalVarBinding(vn,
false )。
- 执行 ? env.CreateGlobalVarBinding(vn,
- 返回
unused 。
与显式的 var 或函数声明不同，直接在
16.2 模块
语法
16.2.1 Module Semantics
16.2.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
LexicallyDeclaredNames ofModuleItemList contains any duplicate entries. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofModuleItemList also occurs in theVarDeclaredNames ofModuleItemList . -
It is a Syntax Error if the
ExportedNames ofModuleItemList contains any duplicate entries. -
It is a Syntax Error if any element of the
ExportedBindings ofModuleItemList does not also occur in either theVarDeclaredNames ofModuleItemList , or theLexicallyDeclaredNames ofModuleItemList . -
It is a Syntax Error if
ModuleItemList Contains super. -
It is a Syntax Error if
ModuleItemList Contains NewTarget . -
It is a Syntax Error if
ContainsDuplicateLabels ofModuleItemList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedBreakTarget ofModuleItemList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedContinueTarget ofModuleItemList with arguments « » and « » istrue . -
It is a Syntax Error if
AllPrivateIdentifiersValid ofModuleItemList with argument « » isfalse .
The duplicate export default
- It is a Syntax Error if
IsStringWellFormedUnicode (theSV ofStringLiteral ) isfalse .
16.2.1.2 Static Semantics: ImportedLocalNames ( importEntries )
The abstract operation ImportedLocalNames takes argument importEntries (a
- Let localNames be a new empty
List . - For each
ImportEntry Record i of importEntries, do- Append i.[[LocalName]] to localNames.
- Return localNames.
16.2.1.3 Static Semantics: ModuleRequests
The
- Return a new empty
List .
- Return
ModuleRequests ofModuleItem .
- Let moduleNames be
ModuleRequests ofModuleItemList . - Let additionalNames be
ModuleRequests ofModuleItem . - For each String name of
additionalNames,
do
- If moduleNames does not contain
name,
then
- Append name to moduleNames.
- If moduleNames does not contain
name,
then
- Return moduleNames.
- Return a new empty
List .
- Return
ModuleRequests ofFromClause .
- Return a
List whose sole element is theSV ofStringLiteral .
- Return the
ModuleRequests ofFromClause .
- Return a new empty
List .
16.2.1.4 Abstract Module Records
A Module Record encapsulates structural information about the imports and exports of a single module. This information is used to link the imports and exports of sets of connected modules. A Module Record includes four fields that are only used when evaluating a module.
For specification purposes Module Record values are values of the
Module Record defines the fields listed in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Realm]] |
a |
The |
| [[Environment]] |
a |
The |
| [[Namespace]] |
an Object or |
The Module Namespace Object ( |
| [[HostDefined]] |
anything (default value is |
Field reserved for use by |
| Method | Purpose |
|---|---|
| LoadRequestedModules( [ hostDefined ] ) |
Prepares the module for linking by recursively loading all its dependencies, and returns a promise. |
| GetExportedNames([exportStarSet]) |
Return a list of all names that are either directly or indirectly exported from this module. LoadRequestedModules must have completed successfully prior to invoking this method. |
| ResolveExport(exportName [, resolveSet]) |
Return the binding of a name exported by this module. Bindings are represented by a ResolvedBinding
Record, of the form { [[Module]]: Each time this operation is called with a specific exportName, resolveSet pair as arguments it must return the same result. LoadRequestedModules must have completed successfully prior to invoking this method. |
| Link() |
Prepare the module for evaluation by transitively resolving all module dependencies and
creating a LoadRequestedModules must have completed successfully prior to invoking this method. |
| Evaluate() |
Returns a promise for the evaluation of this module and its dependencies, resolving on
successful evaluation or if it has already been evaluated successfully, and rejecting for
an
evaluation error or if it has already been evaluated unsuccessfully. If the promise is
rejected, Link must have completed successfully prior to invoking this method. |
16.2.1.5 Cyclic Module Records
A Cyclic Module
Record is used to represent information about a module that can participate in dependency
cycles
with other modules that are subclasses of the
In addition to the fields defined in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Status]] |
|
Initially |
| [[EvaluationError]] |
a |
A |
| [[DFSIndex]] |
an |
Auxiliary field used during Link and Evaluate only. If [[Status]]
is
either |
| [[DFSAncestorIndex]] |
an |
Auxiliary field used during Link and Evaluate only. If [[Status]]
is
either |
| [[RequestedModules]] |
a |
A |
| [[LoadedModules]] |
a |
A map from the specifier strings used by the module represented by this record to request
the
importation of a module to the resolved |
| [[CycleRoot]] |
a |
The first visited module of the cycle, the root DFS ancestor of the strongly connected component. For a module not in a cycle, this would be the module itself. Once Evaluate has completed, a module's [[DFSAncestorIndex]] is the [[DFSIndex]] of its [[CycleRoot]]. |
| [[HasTLA]] | a Boolean |
Whether this module is individually asynchronous (for example, if it's a |
| [[AsyncEvaluation]] | a Boolean |
Whether this module is either itself asynchronous or has an asynchronous dependency. Note:
The
order in which this field is set is used to order queued executions, see |
| [[TopLevelCapability]] |
a |
If this module is the [[CycleRoot]] of some cycle, and Evaluate()
was
called on some module in that cycle, this field contains the |
| [[AsyncParentModules]] |
a |
If this module or a dependency has [[HasTLA]]
|
| [[PendingAsyncDependencies]] |
an |
If this module has any asynchronous dependencies, this tracks the number of asynchronous dependency modules remaining to execute for this module. A module with asynchronous dependencies will be executed when this field reaches 0 and there are no execution errors. |
In addition to the methods defined in
| Method | Purpose |
|---|---|
| InitializeEnvironment() |
Initialize the |
| ExecuteModule( [ promiseCapability ] ) |
Evaluate the module's code within its |
A GraphLoadingState
Record is a
| Field Name | Value Type | Meaning |
|---|---|---|
| [[PromiseCapability]] |
a |
The promise to resolve when the loading process finishes. |
| [[IsLoading]] | a Boolean | It is true if the loading process has not finished yet, neither successfully nor with an error. |
| [[PendingModulesCount]] |
a non-negative |
It tracks the number of pending |
| [[Visited]] |
a |
It is a list of the |
| [[HostDefined]] |
anything (default value is |
It contains |
16.2.1.5.1 LoadRequestedModules ( [ hostDefined ] )
The LoadRequestedModules concrete method of a
- If hostDefined is not present, let
hostDefined be
empty . - Let pc be !
NewPromiseCapability (%Promise% ). - Let state be the
GraphLoadingState Record { [[IsLoading]]:true , [[PendingModulesCount]]: 1, [[Visited]]: « », [[PromiseCapability]]: pc, [[HostDefined]]: hostDefined }. - Perform
InnerModuleLoading (state, module). - Return pc.[[Promise]].
<link rel="preload" as="..."> tags.
import() expressions never set the hostDefined parameter.
16.2.1.5.1.1 InnerModuleLoading ( state, module )
The abstract operation InnerModuleLoading takes arguments state (a
Assert : state.[[IsLoading]] istrue .- If module is a
Cyclic Module Record , module.[[Status]] isnew , and state.[[Visited]] does not contain module, then- Append module to state.[[Visited]].
- Let requestedModulesCount be the number of elements in module.[[RequestedModules]].
- Set state.[[PendingModulesCount]] to state.[[PendingModulesCount]] + requestedModulesCount.
- For each String required of
module.[[RequestedModules]], do
- If module.[[LoadedModules]] contains a
Record whose [[Specifier]] is required, then- Let record be that
Record . - Perform
InnerModuleLoading (state, record.[[Module]]).
- Let record be that
- Else,
- Perform
HostLoadImportedModule (module, required, state.[[HostDefined]], state). - NOTE:
HostLoadImportedModule will callFinishLoadingImportedModule , which re-enters the graph loading process throughContinueModuleLoading .
- Perform
- If state.[[IsLoading]] is
false , returnunused .
- If module.[[LoadedModules]] contains a
Assert : state.[[PendingModulesCount]] ≥ 1.- Set state.[[PendingModulesCount]] to state.[[PendingModulesCount]] - 1.
- If state.[[PendingModulesCount]] = 0, then
- Set state.[[IsLoading]] to
false . - For each
Cyclic Module Record loaded of state.[[Visited]], do- If loaded.[[Status]] is
new , set loaded.[[Status]] tounlinked .
- If loaded.[[Status]] is
- Perform !
Call (state.[[PromiseCapability]].[[Resolve]],undefined , «undefined »).
- Set state.[[IsLoading]] to
- Return
unused .
16.2.1.5.1.2 ContinueModuleLoading ( state, moduleCompletion )
The abstract operation ContinueModuleLoading takes arguments state (a
- If state.[[IsLoading]]
is
false , returnunused . - If moduleCompletion is a
normal completion , then- Perform
InnerModuleLoading (state, moduleCompletion.[[Value]]).
- Perform
- Else,
- Set state.[[IsLoading]] to
false . - Perform !
Call (state.[[PromiseCapability]].[[Reject]],undefined , « moduleCompletion.[[Value]] »).
- Set state.[[IsLoading]] to
- Return
unused .
16.2.1.5.2 Link ( )
The Link concrete method of a
Assert : module.[[Status]] is one ofunlinked ,linked ,evaluating-async , orevaluated .- Let stack be a new empty
List . - Let result be
Completion (InnerModuleLinking (module, stack, 0)). - If result is an
abrupt completion , then- For each
Cyclic Module Record m of stack, doAssert : m.[[Status]] islinking .- Set m.[[Status]]
to
unlinked .
Assert : module.[[Status]] isunlinked .- Return ? result.
- For each
Assert : module.[[Status]] is one oflinked ,evaluating-async , orevaluated .Assert : stack is empty.- Return
unused .
16.2.1.5.2.1 InnerModuleLinking ( module, stack, index )
The abstract operation InnerModuleLinking takes arguments module (a
- If module is not a
Cyclic Module Record , then- Perform ? module.Link().
- Return index.
- If module.[[Status]]
is
one of
linking ,linked ,evaluating-async , orevaluated , then- Return index.
Assert : module.[[Status]] isunlinked .- Set module.[[Status]]
to
linking . - Set module.[[DFSIndex]] to index.
- Set module.[[DFSAncestorIndex]] to index.
- Set index to index + 1.
- Append module to stack.
- For each String required of
module.[[RequestedModules]], do
- Let requiredModule be
GetImportedModule (module, required). - Set index to ?
InnerModuleLinking (requiredModule, stack, index). - If requiredModule is a
Cyclic Module Record , thenAssert : requiredModule.[[Status]] is one oflinking ,linked ,evaluating-async , orevaluated .Assert : requiredModule.[[Status]] islinking if and only if stack contains requiredModule.- If requiredModule.[[Status]] is
linking , then- Set module.[[DFSAncestorIndex]] to
min (module.[[DFSAncestorIndex]], requiredModule.[[DFSAncestorIndex]]).
- Set module.[[DFSAncestorIndex]] to
- Let requiredModule be
- Perform ? module.InitializeEnvironment().
Assert : module occurs exactly once in stack.Assert : module.[[DFSAncestorIndex]] ≤ module.[[DFSIndex]].- If module.[[DFSAncestorIndex]] = module.[[DFSIndex]], then
- Let done be
false . - Repeat, while done is
false ,- Let requiredModule be the last element of stack.
- Remove the last element of stack.
Assert : requiredModule is aCyclic Module Record .- Set requiredModule.[[Status]] to
linked . - If requiredModule and
module
are the same
Module Record , set done totrue .
- Let done be
- Return index.
16.2.1.5.3 Evaluate ( )
The Evaluate concrete method of a
Assert : This call to Evaluate is not happening at the same time as another call to Evaluate within thesurrounding agent .Assert : module.[[Status]] is one oflinked ,evaluating-async , orevaluated .- If module.[[Status]] is
either
evaluating-async orevaluated , set module to module.[[CycleRoot]]. - If module.[[TopLevelCapability]] is not
empty , then- Return module.[[TopLevelCapability]].[[Promise]].
- Let stack be a new empty
List . - Let capability be !
NewPromiseCapability (%Promise% ). - Set module.[[TopLevelCapability]] to capability.
- Let result be
Completion (InnerModuleEvaluation (module, stack, 0)). - If result is an
abrupt completion , then- For each
Cyclic Module Record m of stack, doAssert : m.[[Status]] isevaluating .- Set m.[[Status]]
to
evaluated . - Set m.[[EvaluationError]] to result.
Assert : module.[[Status]] isevaluated .Assert : module.[[EvaluationError]] is result.- Perform !
Call (capability.[[Reject]],undefined , « result.[[Value]] »).
- For each
- Else,
- Return capability.[[Promise]].
16.2.1.5.3.1 InnerModuleEvaluation ( module, stack, index )
The abstract operation InnerModuleEvaluation takes arguments module (a
- If module is not a
Cyclic Module Record , then- Let promise be ! module.Evaluate().
Assert : promise.[[PromiseState]] is notpending .- If promise.[[PromiseState]] is
rejected , then- Return
ThrowCompletion (promise.[[PromiseResult]]).
- Return
- Return index.
- If module.[[Status]]
is
either
evaluating-async orevaluated , then- If module.[[EvaluationError]] is
empty , return index. - Otherwise, return ? module.[[EvaluationError]].
- If module.[[EvaluationError]] is
- If module.[[Status]]
is
evaluating , return index. Assert : module.[[Status]] islinked .- Set module.[[Status]]
to
evaluating . - Set module.[[DFSIndex]] to index.
- Set module.[[DFSAncestorIndex]] to index.
- Set module.[[PendingAsyncDependencies]] to 0.
- Set index to index + 1.
- Append module to stack.
- For each String required of
module.[[RequestedModules]], do
- Let requiredModule be
GetImportedModule (module, required). - Set index to ?
InnerModuleEvaluation (requiredModule, stack, index). - If requiredModule is a
Cyclic Module Record , thenAssert : requiredModule.[[Status]] is one ofevaluating ,evaluating-async , orevaluated .Assert : requiredModule.[[Status]] isevaluating if and only if stack contains requiredModule.- If requiredModule.[[Status]] is
evaluating , then- Set module.[[DFSAncestorIndex]] to
min (module.[[DFSAncestorIndex]], requiredModule.[[DFSAncestorIndex]]).
- Set module.[[DFSAncestorIndex]] to
- Else,
- Set requiredModule to requiredModule.[[CycleRoot]].
Assert : requiredModule.[[Status]] is eitherevaluating-async orevaluated .- If requiredModule.[[EvaluationError]] is not
empty , return ? requiredModule.[[EvaluationError]].
- If requiredModule.[[AsyncEvaluation]] is
true , then- Set module.[[PendingAsyncDependencies]] to module.[[PendingAsyncDependencies]] + 1.
- Append module to requiredModule.[[AsyncParentModules]].
- Let requiredModule be
- If module.[[PendingAsyncDependencies]] > 0 or module.[[HasTLA]] is
true , thenAssert : module.[[AsyncEvaluation]] isfalse and was never previously set totrue .- Set module.[[AsyncEvaluation]] to
true . - NOTE: The order in which module records have their
[[AsyncEvaluation]] fields transition to
true is significant. (See16.2.1.5.3.4 .) - If module.[[PendingAsyncDependencies]] = 0, perform
ExecuteAsyncModule (module).
- Else,
- Perform ? module.ExecuteModule().
Assert : module occurs exactly once in stack.Assert : module.[[DFSAncestorIndex]] ≤ module.[[DFSIndex]].- If module.[[DFSAncestorIndex]] = module.[[DFSIndex]], then
- Let done be
false . - Repeat, while done is
false ,- Let requiredModule be the last element of stack.
- Remove the last element of stack.
Assert : requiredModule is aCyclic Module Record .- If requiredModule.[[AsyncEvaluation]] is
false , set requiredModule.[[Status]] toevaluated . - Otherwise, set requiredModule.[[Status]] to
evaluating-async . - If requiredModule and
module
are the same
Module Record , set done totrue . - Set requiredModule.[[CycleRoot]] to module.
- Let done be
- Return index.
A module is
Any modules depending on a module of an asynchronous cycle when that cycle is not
16.2.1.5.3.2 ExecuteAsyncModule ( module )
The abstract operation ExecuteAsyncModule takes argument module (a
Assert : module.[[Status]] is eitherevaluating orevaluating-async .Assert : module.[[HasTLA]] istrue .- Let capability be !
NewPromiseCapability (%Promise% ). - Let fulfilledClosure be a new
Abstract Closure with no parameters that captures module and performs the following steps when called:- Perform
AsyncModuleExecutionFulfilled (module). - Return
undefined .
- Perform
- Let onFulfilled be
CreateBuiltinFunction (fulfilledClosure, 0,"" , « »). - Let rejectedClosure be a new
Abstract Closure with parameters (error) that captures module and performs the following steps when called:- Perform
AsyncModuleExecutionRejected (module, error). - Return
undefined .
- Perform
- Let onRejected be
CreateBuiltinFunction (rejectedClosure, 0,"" , « »). - Perform
PerformPromiseThen (capability.[[Promise]], onFulfilled, onRejected). - Perform ! module.ExecuteModule(capability).
- Return
unused .
16.2.1.5.3.3 GatherAvailableAncestors ( module, execList )
The abstract operation GatherAvailableAncestors takes arguments module (a
- For each
Cyclic Module Record m of module.[[AsyncParentModules]], do- If execList does not contain m
and
m.[[CycleRoot]].[[EvaluationError]] is
empty , thenAssert : m.[[Status]] isevaluating-async .Assert : m.[[EvaluationError]] isempty .Assert : m.[[AsyncEvaluation]] istrue .Assert : m.[[PendingAsyncDependencies]] > 0.- Set m.[[PendingAsyncDependencies]] to m.[[PendingAsyncDependencies]] - 1.
- If m.[[PendingAsyncDependencies]] = 0, then
- Append m to execList.
- If m.[[HasTLA]] is
false , performGatherAvailableAncestors (m, execList).
- If execList does not contain m
and
m.[[CycleRoot]].[[EvaluationError]] is
- Return
unused .
When an asynchronous execution for a root module is fulfilled, this function determines the list of modules which are able to synchronously execute together on this completion, populating them in execList.
16.2.1.5.3.4 AsyncModuleExecutionFulfilled ( module )
The abstract operation AsyncModuleExecutionFulfilled takes argument module (a
- If module.[[Status]]
is
evaluated , thenAssert : module.[[EvaluationError]] is notempty .- Return
unused .
Assert : module.[[Status]] isevaluating-async .Assert : module.[[AsyncEvaluation]] istrue .Assert : module.[[EvaluationError]] isempty .- Set module.[[AsyncEvaluation]] to
false . - Set module.[[Status]]
to
evaluated . - If module.[[TopLevelCapability]] is not
empty , then - Let execList be a new empty
List . - Perform
GatherAvailableAncestors (module, execList). - Let sortedExecList be a
List whose elements are the elements of execList, in the order in which they had their [[AsyncEvaluation]] fields set totrue inInnerModuleEvaluation . Assert : All elements of sortedExecList have their [[AsyncEvaluation]] field set totrue , [[PendingAsyncDependencies]] field set to 0, and [[EvaluationError]] field set toempty .- For each
Cyclic Module Record m of sortedExecList, do- If m.[[Status]]
is
evaluated , thenAssert : m.[[EvaluationError]] is notempty .
- Else if m.[[HasTLA]]
is
true , then- Perform
ExecuteAsyncModule (m).
- Perform
- Else,
- Let result be m.ExecuteModule().
- If result is an
abrupt completion , then- Perform
AsyncModuleExecutionRejected (m, result.[[Value]]).
- Perform
- Else,
- If m.[[Status]]
is
- Return
unused .
16.2.1.5.3.5 AsyncModuleExecutionRejected ( module, error )
The abstract operation AsyncModuleExecutionRejected takes arguments module (a
- If module.[[Status]]
is
evaluated , thenAssert : module.[[EvaluationError]] is notempty .- Return
unused .
Assert : module.[[Status]] isevaluating-async .Assert : module.[[AsyncEvaluation]] istrue .Assert : module.[[EvaluationError]] isempty .- Set module.[[EvaluationError]] to
ThrowCompletion (error). - Set module.[[Status]]
to
evaluated . - For each
Cyclic Module Record m of module.[[AsyncParentModules]], do- Perform
AsyncModuleExecutionRejected (m, error).
- Perform
- If module.[[TopLevelCapability]] is not
empty , then - Return
unused .
16.2.1.5.4 Example Cyclic Module Record Graphs
This non-normative section gives a series of examples of the linking and evaluation of a few common module graphs, with a specific focus on how errors can occur.
First consider the following simple module graph:
Let's first assume that there are no error conditions. When a
Consider then cases involving linking errors, after a successful call to
A.LoadRequestedModules(). If
Finally, consider a case involving evaluation errors after a successful call to Link(). If
Now consider a different type of error condition:
In this scenario, module A declares a dependency on some other module, but no
The difference here between loading, linking and evaluation errors is due to the following characteristic:
Evaluation must be only performed once, as it can cause side effects; it is thus important to remember whether evaluation has already been performed, even if unsuccessfully. (In the error case, it makes sense to also remember the exception because otherwise subsequent Evaluate() calls would have to synthesize a new one.)- Linking, on the other hand, is side-effect-free, and thus even if it fails, it can be retried at a later time with no issues.
- Loading closely interacts with the
host , and it may be desiderable for some of them to allow users to retry failed loads (for example, if the failure is caused by temporarily bad network conditions).
Now, consider a module graph with a cycle:
Here we assume that the entry point is module A, so that the
Then the
An analogous story occurs for the evaluation phase of a cyclic module graph, in the success case.
Now consider a case where A has a linking error; for example, it tries to import a
binding
from C that does not exist. In that case, the above steps still occur, including the
early
return from the second call to
Alternatively, consider a case where A has an evaluation error; for example, its source
code
throws an exception. In that case, the evaluation-time analog of the above steps still occurs,
including
the early return from the second call to await through the whole dependency graph through the
Lastly, consider a module graph with a cycle, where all modules complete asynchronously:
Loading and linking happen as before, and all modules end up with [[Status]]
set to
Calling A.Evaluate() calls
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] |
|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 2 (B and C) | ||
| B | 1 | 0 | « A » | 1 (D) | ||
| C | 2 | 0 | « A » | 2 (D and E) | ||
| D | 3 | 0 | « B, C » | 0 | ||
| E | 4 | 4 | « C » | 0 |
Let us assume that E finishes executing first. When that happens,
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] |
|---|---|---|---|---|---|---|
| C | 2 | 0 | « A » | 1 (D) | ||
| E | 4 | 4 | « C » | 0 |
D is next to finish (as it was the only module that was still executing). When that
happens,
await). The fields of the updated modules are as given in
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] |
|---|---|---|---|---|---|---|
| B | 1 | 0 | « A » | 0 | ||
| C | 2 | 0 | « A » | 0 | ||
| D | 3 | 0 | « B, C » | 0 |
Let us assume that C finishes executing next. When that happens,
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] |
|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 1 (B) | ||
| C | 2 | 0 | « A » | 0 |
Then, B finishes executing. When that happens,
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] |
|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 0 | ||
| B | 1 | 0 | « A » | 0 |
Finally, A finishes executing. When that happens,
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] |
|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 0 |
Alternatively, consider a failure case where C fails execution and returns an error
before
B has finished executing. When that happens,
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] | [[EvaluationError]] |
|---|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 1 (B) | |||
| C | 2 | 1 | « A » | 0 | C's evaluation error |
A will be rejected with the same error as C since C will call
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] | [[EvaluationError]] |
|---|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 0 | C's |
Then, B finishes executing without an error. When that happens,
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] | [[EvaluationError]] |
|---|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 0 | C's |
||
| B | 1 | 0 | « A » | 0 |
16.2.1.6 Source Text Module Records
A Source Text
Module
Record is used to represent information about a module that was defined from
A
In addition to the fields defined in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ECMAScriptCode]] |
a |
The result of parsing the source text of this module using |
| [[Context]] |
an |
The |
| [[ImportMeta]] |
an Object or |
An object exposed through the import.meta meta property. It is
|
| [[ImportEntries]] |
a |
A |
| [[LocalExportEntries]] |
a |
A |
| [[IndirectExportEntries]] |
a |
A export * as namespace
declarations.
|
| [[StarExportEntries]] |
a |
A export * declarations that occur within the module, not including
export * as namespace declarations.
|
An ImportEntry Record
is
a
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ModuleRequest]] | a String |
String value of the |
| [[ImportName]] |
a String or |
The name under which the desired binding is exported by the module identified by [[ModuleRequest]]. The value |
| [[LocalName]] | a String | The name that is used to locally access the imported value from within the importing module. |
| Import Statement Form | [[ModuleRequest]] | [[ImportName]] | [[LocalName]] |
|---|---|---|---|
import v from "mod";
|
|
|
|
import * as ns from "mod";
|
|
|
|
import {x} from "mod";
|
|
|
|
import {x as v} from "mod";
|
|
|
|
import "mod";
|
An |
||
An ExportEntry Record
is
a
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ExportName]] |
a String or |
The name used to export this binding by this module. |
| [[ModuleRequest]] |
a String or |
The String value of the |
| [[ImportName]] |
a String, |
The name under which the desired binding is exported by the module identified by [[ModuleRequest]]. export * as ns from "mod" declarations.
export * from "mod"
declarations.
|
| [[LocalName]] |
a String or |
The name that is used to locally access the exported value from within the importing module.
|
| Export Statement Form | [[ExportName]] | [[ModuleRequest]] | [[ImportName]] | [[LocalName]] |
|---|---|---|---|---|
export var v;
|
|
|
|
|
export default function f() {}
|
|
|
|
|
export default function () {}
|
|
|
|
|
export default 42;
|
|
|
|
|
export {x};
|
|
|
|
|
export {v as x};
|
|
|
|
|
export {x} from "mod";
|
|
|
|
|
export {v as x} from "mod";
|
|
|
|
|
export * from "mod";
|
|
|
|
|
export * as ns from "mod";
|
|
|
|
|
The following definitions specify the required concrete methods and other
16.2.1.6.1 ParseModule ( sourceText, realm, hostDefined )
The abstract operation ParseModule takes arguments sourceText (
- Let body be
ParseText (sourceText,Module ). - If body is a
List of errors, return body. - Let requestedModules be the
ModuleRequests of body. - Let importEntries be
ImportEntries of body. - Let importedBoundNames be
ImportedLocalNames (importEntries). - Let indirectExportEntries be a new empty
List . - Let localExportEntries be a new empty
List . - Let starExportEntries be a new empty
List . - Let exportEntries be
ExportEntries of body. - For each
ExportEntry Record ee of exportEntries, do- If ee.[[ModuleRequest]]
is
null , then- If importedBoundNames does not contain
ee.[[LocalName]], then
- Append ee to localExportEntries.
- Else,
- Let ie be the element of importEntries whose [[LocalName]] is ee.[[LocalName]].
- If ie.[[ImportName]] is
namespace-object , then- NOTE: This is a re-export of an imported module namespace object.
- Append ee to localExportEntries.
- Else,
- NOTE: This is a re-export of a single name.
- Append the
ExportEntry Record { [[ModuleRequest]]: ie.[[ModuleRequest]], [[ImportName]]: ie.[[ImportName]], [[LocalName]]:null , [[ExportName]]: ee.[[ExportName]] } to indirectExportEntries.
- If importedBoundNames does not contain
ee.[[LocalName]], then
- Else if ee.[[ImportName]] is
all-but-default , thenAssert : ee.[[ExportName]] isnull .- Append ee to starExportEntries.
- Else,
- Append ee to indirectExportEntries.
- If ee.[[ModuleRequest]]
is
- Let async be body
Contains await. - Return
Source Text Module Record { [[Realm]]: realm, [[Environment]]:empty , [[Namespace]]:empty , [[CycleRoot]]:empty , [[HasTLA]]: async, [[AsyncEvaluation]]:false , [[TopLevelCapability]]:empty , [[AsyncParentModules]]: « », [[PendingAsyncDependencies]]:empty , [[Status]]:new , [[EvaluationError]]:empty , [[HostDefined]]: hostDefined, [[ECMAScriptCode]]: body, [[Context]]:empty , [[ImportMeta]]:empty , [[RequestedModules]]: requestedModules, [[LoadedModules]]: « », [[ImportEntries]]: importEntries, [[LocalExportEntries]]: localExportEntries, [[IndirectExportEntries]]: indirectExportEntries, [[StarExportEntries]]: starExportEntries, [[DFSIndex]]:empty , [[DFSAncestorIndex]]:empty }.
An implementation may parse module source text and analyse it for Early Error conditions prior to the evaluation of ParseModule for that module source text. However, the reporting of any errors must be deferred until the point where this specification actually performs ParseModule upon that source text.
16.2.1.6.2 GetExportedNames ( [ exportStarSet ] )
The GetExportedNames concrete method of a
Assert : module.[[Status]] is notnew .- If exportStarSet is not present, set
exportStarSet to a new empty
List . - If exportStarSet contains module, then
- Append module to exportStarSet.
- Let exportedNames be a new empty
List . - For each
ExportEntry Record e of module.[[LocalExportEntries]], do - For each
ExportEntry Record e of module.[[IndirectExportEntries]], do - For each
ExportEntry Record e of module.[[StarExportEntries]], doAssert : e.[[ModuleRequest]] is notnull .- Let requestedModule be
GetImportedModule (module, e.[[ModuleRequest]]). - Let starNames be requestedModule.GetExportedNames(exportStarSet).
- For each element n of starNames,
do
- If
SameValue (n,"default" ) isfalse , then- If exportedNames does not contain
n, then
- Append n to exportedNames.
- If exportedNames does not contain
n, then
- If
- Return exportedNames.
GetExportedNames does not filter out or throw an exception for names that have ambiguous star export bindings.
16.2.1.6.3 ResolveExport ( exportName [ , resolveSet ] )
The ResolveExport concrete method of a
ResolveExport attempts to resolve an imported binding to the actual defining module and local
binding
name. The defining module may be the module represented by the
If a defining module is found, a
It performs the following steps when called:
Assert : module.[[Status]] is notnew .- If resolveSet is not present, set
resolveSet to a new empty
List . - For each
Record { [[Module]], [[ExportName]] } r of resolveSet, do- If module and r.[[Module]] are the same
Module Record andSameValue (exportName, r.[[ExportName]]) istrue , thenAssert : This is a circular import request.- Return
null .
- If module and r.[[Module]] are the same
- Append the
Record { [[Module]]: module, [[ExportName]]: exportName } to resolveSet. - For each
ExportEntry Record e of module.[[LocalExportEntries]], do- If
SameValue (exportName, e.[[ExportName]]) istrue , thenAssert : module provides the direct binding for this export.- Return
ResolvedBinding Record { [[Module]]: module, [[BindingName]]: e.[[LocalName]] }.
- If
- For each
ExportEntry Record e of module.[[IndirectExportEntries]], do- If
SameValue (exportName, e.[[ExportName]]) istrue , thenAssert : e.[[ModuleRequest]] is notnull .- Let importedModule be
GetImportedModule (module, e.[[ModuleRequest]]). - If e.[[ImportName]] is
all , thenAssert : module does not provide the direct binding for this export.- Return
ResolvedBinding Record { [[Module]]: importedModule, [[BindingName]]:namespace }.
- Else,
Assert : module imports a specific binding for this export.- Return importedModule.ResolveExport(e.[[ImportName]], resolveSet).
- If
- If
SameValue (exportName,"default" ) istrue , thenAssert : Adefaultexport was not explicitly defined by this module.- Return
null . - NOTE: A
defaultexport cannot be provided by anexport * from "mod"declaration.
- Let starResolution be
null . - For each
ExportEntry Record e of module.[[StarExportEntries]], doAssert : e.[[ModuleRequest]] is notnull .- Let importedModule be
GetImportedModule (module, e.[[ModuleRequest]]). - Let resolution be importedModule.ResolveExport(exportName, resolveSet).
- If resolution is
ambiguous , returnambiguous . - If resolution is not
null , thenAssert : resolution is aResolvedBinding Record .- If starResolution is
null , then- Set starResolution to resolution.
- Else,
Assert : There is more than one*import that includes the requested name.- If resolution.[[Module]] and starResolution.[[Module]] are not the same
Module Record , returnambiguous . - If resolution.[[BindingName]] is not starResolution.[[BindingName]] and either resolution.[[BindingName]] or starResolution.[[BindingName]] is
namespace , returnambiguous . - If resolution.[[BindingName]]
is a String , starResolution.[[BindingName]]is a String , andSameValue (resolution.[[BindingName]], starResolution.[[BindingName]]) isfalse , returnambiguous .
- Return starResolution.
16.2.1.6.4 InitializeEnvironment ( )
The InitializeEnvironment concrete method of a
- For each
ExportEntry Record e of module.[[IndirectExportEntries]], doAssert : e.[[ExportName]] is notnull .- Let resolution be module.ResolveExport(e.[[ExportName]]).
- If resolution is either
null orambiguous , throw aSyntaxError exception. Assert : resolution is aResolvedBinding Record .
Assert : All named exports from module are resolvable.- Let realm be module.[[Realm]].
Assert : realm is notundefined .- Let env be
NewModuleEnvironment (realm.[[GlobalEnv]]). - Set module.[[Environment]] to env.
- For each
ImportEntry Record in of module.[[ImportEntries]], do- Let importedModule be
GetImportedModule (module, in.[[ModuleRequest]]). - If in.[[ImportName]]
is
namespace-object , then- Let namespace be
GetModuleNamespace (importedModule). - Perform
! env.CreateImmutableBinding(in.[[LocalName]],
true ). - Perform ! env.InitializeBinding(in.[[LocalName]], namespace).
- Let namespace be
- Else,
- Let resolution be importedModule.ResolveExport(in.[[ImportName]]).
- If resolution is either
null orambiguous , throw aSyntaxError exception. - If resolution.[[BindingName]] is
namespace , then- Let namespace be
GetModuleNamespace (resolution.[[Module]]). - Perform
! env.CreateImmutableBinding(in.[[LocalName]],
true ). - Perform ! env.InitializeBinding(in.[[LocalName]], namespace).
- Let namespace be
- Else,
- Perform env.CreateImportBinding(in.[[LocalName]], resolution.[[Module]], resolution.[[BindingName]]).
- Let importedModule be
- Let moduleContext be a new
ECMAScript code execution context . - Set the Function of moduleContext to
null . Assert : module.[[Realm]] is notundefined .- Set the
Realm of moduleContext to module.[[Realm]]. - Set the ScriptOrModule of moduleContext to module.
- Set the VariableEnvironment of moduleContext to module.[[Environment]].
- Set the LexicalEnvironment of moduleContext to module.[[Environment]].
- Set the PrivateEnvironment of moduleContext to
null . - Set module.[[Context]] to moduleContext.
- Push moduleContext onto the
execution context stack ; moduleContext is now therunning execution context . - Let code be module.[[ECMAScriptCode]].
- Let varDeclarations be the
VarScopedDeclarations of code. - Let declaredVarNames be a new empty
List . - For each element d of
varDeclarations,
do
- For each element dn of the
BoundNames of d, do- If declaredVarNames does not contain
dn, then
- Perform
! env.CreateMutableBinding(dn,
false ). - Perform
! env.InitializeBinding(dn,
undefined ). - Append dn to declaredVarNames.
- Perform
! env.CreateMutableBinding(dn,
- If declaredVarNames does not contain
dn, then
- For each element dn of the
- Let lexDeclarations be the
LexicallyScopedDeclarations of code. - Let privateEnv be
null . - For each element d of
lexDeclarations,
do
- For each element dn of the
BoundNames of d, do- If
IsConstantDeclaration of d istrue , then- Perform
! env.CreateImmutableBinding(dn,
true ).
- Perform
! env.CreateImmutableBinding(dn,
- Else,
- Perform
! env.CreateMutableBinding(dn,
false ).
- Perform
! env.CreateMutableBinding(dn,
- If d is either a
FunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration , then- Let fo be
InstantiateFunctionObject of d with arguments env and privateEnv. - Perform ! env.InitializeBinding(dn, fo).
- Let fo be
- If
- For each element dn of the
- Remove moduleContext from the
execution context stack . - Return
unused .
16.2.1.6.5 ExecuteModule ( [ capability ] )
The ExecuteModule concrete method of a
- Let moduleContext be a new
ECMAScript code execution context . - Set the Function of moduleContext to
null . - Set the
Realm of moduleContext to module.[[Realm]]. - Set the ScriptOrModule of moduleContext to module.
Assert : module has been linked and declarations in its module environment have been instantiated.- Set the VariableEnvironment of moduleContext to module.[[Environment]].
- Set the LexicalEnvironment of moduleContext to module.[[Environment]].
- Suspend the
running execution context . - If module.[[HasTLA]] is
false , thenAssert : capability is not present.- Push moduleContext onto the
execution context stack ; moduleContext is now therunning execution context . - Let result be
Completion (Evaluation of module.[[ECMAScriptCode]]). - Suspend moduleContext and remove it from the
execution context stack . - Resume the context that is now on the top of the
execution context stack as therunning execution context . - If result is an
abrupt completion , then- Return ? result.
- Else,
Assert : capability is aPromiseCapability Record .- Perform
AsyncBlockStart (capability, module.[[ECMAScriptCode]], moduleContext).
- Return
unused .
16.2.1.7 GetImportedModule ( referrer, specifier )
The abstract operation GetImportedModule takes arguments referrer (a
Assert : Exactly one element of referrer.[[LoadedModules]] is aRecord whose [[Specifier]] is specifier, since LoadRequestedModules has completed successfully on referrer prior to invoking this abstract operation.- Let record be the
Record in referrer.[[LoadedModules]] whose [[Specifier]] is specifier. - Return record.[[Module]].
16.2.1.8 HostLoadImportedModule ( referrer, specifier, hostDefined, payload )
The
An example of when referrer can be a
<button type="button" onclick="import('./foo.mjs')">Click me</button>there will be no import()
An implementation of HostLoadImportedModule must conform to the following requirements:
-
The
host environment must performFinishLoadingImportedModule (referrer, specifier, payload, result), where result is either anormal completion containing the loadedModule Record or athrow completion , either synchronously or asynchronously. -
If this operation is called multiple times with the same (referrer, specifier)
pair and it performs
FinishLoadingImportedModule (referrer, specifier, payload, result) where result is anormal completion , then it must performFinishLoadingImportedModule (referrer, specifier, payload, result) with the same result each time. -
The operation must treat payload as an opaque value to be passed through to
FinishLoadingImportedModule .
The actual process performed is
16.2.1.9 FinishLoadingImportedModule ( referrer, specifier, payload, result )
The abstract operation FinishLoadingImportedModule takes arguments referrer (a
- If result is a
normal completion , then - If payload is a
GraphLoadingState Record , then- Perform
ContinueModuleLoading (payload, result).
- Perform
- Else,
- Perform
ContinueDynamicImport (payload, result).
- Perform
- Return
unused .
16.2.1.10 GetModuleNamespace ( module )
The abstract operation GetModuleNamespace takes argument module (an instance of a concrete
subclass of
Assert : If module is aCyclic Module Record , then module.[[Status]] is notnew orunlinked .- Let namespace be module.[[Namespace]].
- If namespace is
empty , then- Let exportedNames be module.GetExportedNames().
- Let unambiguousNames be a new empty
List . - For each element name of
exportedNames,
do
- Let resolution be module.ResolveExport(name).
- If resolution is a
ResolvedBinding Record , append name to unambiguousNames.
- Set namespace to
ModuleNamespaceCreate (module, unambiguousNames).
- Return namespace.
GetModuleNamespace never throws. Instead, unresolvable names are simply excluded from the namespace at this point. They will lead to a real linking error later unless they are all ambiguous star exports that are not explicitly requested anywhere.
16.2.1.11 Runtime Semantics: Evaluation
- Return
undefined .
- Let result be
Completion (Evaluation ofModuleItemList ). - If result is a
normal completion and result.[[Value]] isempty , then- Return
undefined .
- Return
- Return ? result.
- Let sl be ?
Evaluation ofModuleItemList . - Let s be
Completion (Evaluation ofModuleItem ). - Return ?
UpdateEmpty (s, sl).
The value of a
- Return
empty .
16.2.2 Imports
Syntax
16.2.2.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
BoundNames ofImportDeclaration contains any duplicate entries.
16.2.2.2 Static Semantics: ImportEntries
The
- Return a new empty
List .
- Let entries1 be
ImportEntries ofModuleItemList . - Let entries2 be
ImportEntries ofModuleItem . - Return the
list-concatenation of entries1 and entries2.
- Return a new empty
List .
- Let module be the sole element of
ModuleRequests ofFromClause . - Return
ImportEntriesForModule ofImportClause with argument module.
- Return a new empty
List .
16.2.2.3 Static Semantics: ImportEntriesForModule
The
- Let entries1 be
ImportEntriesForModule ofImportedDefaultBinding with argument module. - Let entries2 be
ImportEntriesForModule ofNameSpaceImport with argument module. - Return the
list-concatenation of entries1 and entries2.
- Let entries1 be
ImportEntriesForModule ofImportedDefaultBinding with argument module. - Let entries2 be
ImportEntriesForModule ofNamedImports with argument module. - Return the
list-concatenation of entries1 and entries2.
- Let localName be the sole element of
BoundNames ofImportedBinding . - Let defaultEntry be the
ImportEntry Record { [[ModuleRequest]]: module, [[ImportName]]:"default" , [[LocalName]]: localName }. - Return « defaultEntry ».
- Let localName be the
StringValue ofImportedBinding . - Let entry be the
ImportEntry Record { [[ModuleRequest]]: module, [[ImportName]]:namespace-object , [[LocalName]]: localName }. - Return « entry ».
- Return a new empty
List .
- Let specs1 be the
ImportEntriesForModule ofImportsList with argument module. - Let specs2 be the
ImportEntriesForModule ofImportSpecifier with argument module. - Return the
list-concatenation of specs1 and specs2.
- Let localName be the sole element of
BoundNames ofImportedBinding . - Let entry be the
ImportEntry Record { [[ModuleRequest]]: module, [[ImportName]]: localName, [[LocalName]]: localName }. - Return « entry ».
- Let importName be the
StringValue ofModuleExportName . - Let localName be the
StringValue ofImportedBinding . - Let entry be the
ImportEntry Record { [[ModuleRequest]]: module, [[ImportName]]: importName, [[LocalName]]: localName }. - Return « entry ».
16.2.3 Exports
Syntax
16.2.3.1 Static Semantics: Early Errors
-
It is a Syntax Error if
ReferencedBindings ofNamedExports contains anyStringLiteral s. -
For each
IdentifierName n inReferencedBindings ofNamedExports : It is a Syntax Error ifStringValue of n is aReservedWord or theStringValue of n is one of"implements" ,"interface" ,"let" ,"package" ,"private" ,"protected" ,"public" , or"static" .
The above rule means that each
16.2.3.2 Static Semantics: ExportedBindings
The
ExportedBindings are the locally bound names that are explicitly associated with a
It is defined piecewise over the following productions:
- Let names1 be
ExportedBindings ofModuleItemList . - Let names2 be
ExportedBindings ofModuleItem . - Return the
list-concatenation of names1 and names2.
- Return a new empty
List .
- Return a new empty
List .
- Return the
ExportedBindings ofNamedExports .
- Return the
BoundNames ofVariableStatement .
- Return the
BoundNames ofDeclaration .
- Return the
BoundNames of thisExportDeclaration .
- Return a new empty
List .
- Let names1 be the
ExportedBindings ofExportsList . - Let names2 be the
ExportedBindings ofExportSpecifier . - Return the
list-concatenation of names1 and names2.
- Return a
List whose sole element is theStringValue ofModuleExportName .
- Return a
List whose sole element is theStringValue of the firstModuleExportName .
16.2.3.3 Static Semantics: ExportedNames
The
ExportedNames are the externally visible names that a
It is defined piecewise over the following productions:
- Let names1 be
ExportedNames ofModuleItemList . - Let names2 be
ExportedNames ofModuleItem . - Return the
list-concatenation of names1 and names2.
- Return the
ExportedNames ofExportDeclaration .
- Return a new empty
List .
- Return the
ExportedNames ofExportFromClause .
- Return a new empty
List .
- Return a
List whose sole element is theStringValue ofModuleExportName .
- Return the
ExportedNames ofNamedExports .
- Return the
BoundNames ofVariableStatement .
- Return the
BoundNames ofDeclaration .
- Return «
"default" ».
- Return a new empty
List .
- Let names1 be the
ExportedNames ofExportsList . - Let names2 be the
ExportedNames ofExportSpecifier . - Return the
list-concatenation of names1 and names2.
- Return a
List whose sole element is theStringValue ofModuleExportName .
- Return a
List whose sole element is theStringValue of the secondModuleExportName .
16.2.3.4 Static Semantics: ExportEntries
The
- Return a new empty
List .
- Let entries1 be
ExportEntries ofModuleItemList . - Let entries2 be
ExportEntries ofModuleItem . - Return the
list-concatenation of entries1 and entries2.
- Return a new empty
List .
- Let module be the sole element of
ModuleRequests ofFromClause . - Return
ExportEntriesForModule ofExportFromClause with argument module.
- Return
ExportEntriesForModule ofNamedExports with argumentnull .
- Let entries be a new empty
List . - Let names be the
BoundNames ofVariableStatement . - For each element name of names, do
- Append the
ExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]: name, [[ExportName]]: name } to entries.
- Append the
- Return entries.
- Let entries be a new empty
List . - Let names be the
BoundNames ofDeclaration . - For each element name of names, do
- Append the
ExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]: name, [[ExportName]]: name } to entries.
- Append the
- Return entries.
- Let names be
BoundNames ofHoistableDeclaration . - Let localName be the sole element of names.
- Return a
List whose sole element is a newExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]: localName, [[ExportName]]:"default" }.
- Let names be
BoundNames ofClassDeclaration . - Let localName be the sole element of names.
- Return a
List whose sole element is a newExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]: localName, [[ExportName]]:"default" }.
- Let entry be the
ExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]:"*default*" , [[ExportName]]:"default" }. - Return « entry ».
16.2.3.5 Static Semantics: ExportEntriesForModule
The
- Let entry be the
ExportEntry Record { [[ModuleRequest]]: module, [[ImportName]]:all-but-default , [[LocalName]]:null , [[ExportName]]:null }. - Return « entry ».
- Let exportName be the
StringValue ofModuleExportName . - Let entry be the
ExportEntry Record { [[ModuleRequest]]: module, [[ImportName]]:all , [[LocalName]]:null , [[ExportName]]: exportName }. - Return « entry ».
- Return a new empty
List .
- Let specs1 be the
ExportEntriesForModule ofExportsList with argument module. - Let specs2 be the
ExportEntriesForModule ofExportSpecifier with argument module. - Return the
list-concatenation of specs1 and specs2.
- Let sourceName be the
StringValue ofModuleExportName . - If module is
null , then- Let localName be sourceName.
- Let importName be
null .
- Else,
- Let localName be
null . - Let importName be sourceName.
- Let localName be
- Return a
List whose sole element is a newExportEntry Record { [[ModuleRequest]]: module, [[ImportName]]: importName, [[LocalName]]: localName, [[ExportName]]: sourceName }.
- Let sourceName be the
StringValue of the firstModuleExportName . - Let exportName be the
StringValue of the secondModuleExportName . - If module is
null , then- Let localName be sourceName.
- Let importName be
null .
- Else,
- Let localName be
null . - Let importName be sourceName.
- Let localName be
- Return a
List whose sole element is a newExportEntry Record { [[ModuleRequest]]: module, [[ImportName]]: importName, [[LocalName]]: localName, [[ExportName]]: exportName }.
16.2.3.6 Static Semantics: ReferencedBindings
The
- Return a new empty
List .
- Let names1 be the
ReferencedBindings ofExportsList . - Let names2 be the
ReferencedBindings ofExportSpecifier . - Return the
list-concatenation of names1 and names2.
- Return the
ReferencedBindings of the firstModuleExportName .
- Return a
List whose sole element is theIdentifierName .
- Return a
List whose sole element is theStringLiteral .
16.2.3.7 Runtime Semantics: Evaluation
- Return
empty .
- Return ?
Evaluation ofVariableStatement .
- Return ?
Evaluation ofDeclaration .
- Return ?
Evaluation ofHoistableDeclaration .
- Let value be ?
BindingClassDeclarationEvaluation ofClassDeclaration . - Let className be the sole element of
BoundNames ofClassDeclaration . - If className is
"*default*" , then- Let env be the
running execution context 's LexicalEnvironment. - Perform ?
InitializeBoundName ("*default*" , value, env).
- Let env be the
- Return
empty .
- If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue , then- Let value be ?
NamedEvaluation ofAssignmentExpression with argument"default" .
- Let value be ?
- Else,
- Let rhs be ?
Evaluation ofAssignmentExpression . - Let value be ?
GetValue (rhs).
- Let rhs be ?
- Let env be the
running execution context 's LexicalEnvironment. - Perform ?
InitializeBoundName ("*default*" , value, env). - Return
empty .
17 Error Handling and Language Extensions
An implementation must report most errors at the time the relevant ECMAScript language construct is
evaluated.
An early error is an error that can be
detected and reported prior to the evaluation of any construct in the eval is called and
prevent
evaluation of the eval code. All errors that are not
An implementation must report as an
An implementation shall not treat other kinds of errors as
An implementation shall report all errors as specified, except for the following:
-
Except as restricted in
17.1 , ahost or implementation may extendScript syntax,Module syntax, and regular expression pattern or flag syntax. To permit this, all operations (such as callingeval, using a regular expression literal, or using the Function or RegExpconstructor ) that are allowed to throwSyntaxError are permitted to exhibithost-defined behaviour instead of throwingSyntaxError when they encounter ahost-defined extension to the script syntax or regular expression pattern or flag syntax. -
Except as restricted in
17.1 , ahost or implementation may provide additional types, values, objects, properties, and functions beyond those described in this specification. This may cause constructs (such as looking up a variable in the global scope) to havehost-defined behaviour instead of throwing an error (such asReferenceError ).
17.1 Forbidden Extensions
An implementation must not extend this specification in the following ways:
-
ECMAScript
function objects defined using syntacticconstructors instrict mode code must not be created with own properties named"caller" or"arguments" . Such own properties also must not be created forfunction objects defined using anArrowFunction ,MethodDefinition ,GeneratorDeclaration ,GeneratorExpression ,AsyncGeneratorDeclaration ,AsyncGeneratorExpression ,ClassDeclaration ,ClassExpression ,AsyncFunctionDeclaration ,AsyncFunctionExpression , orAsyncArrowFunction regardless of whether the definition is contained instrict mode code . Built-in functions,strict functions created using the Functionconstructor , generator functions created using the Generatorconstructor , async functions created using the AsyncFunctionconstructor , and functions created using thebindmethod also must not be created with such own properties. -
If an implementation extends any
function object with an own property named"caller" the value of that property, as observed using [[Get]] or [[GetOwnProperty]], must not be astrict function object. If it is anaccessor property , the function that is the value of the property's [[Get]] attribute must never return astrict function when called. -
Neither mapped nor unmapped arguments objects may be created with an own property named
"caller" . -
The behaviour of built-in methods which are specified in ECMA-402, such as those named
toLocaleString, must not be extended except as specified in ECMA-402. -
The RegExp pattern grammars in
22.2.1 andB.1.2 must not be extended to recognize any of the source characters A-Z or a-z asIdentityEscape when the [UnicodeMode] grammar parameter is present.[+UnicodeMode] -
The Syntactic Grammar must not be extended in any manner that allows the token
:to immediately follow source text that is matched by theBindingIdentifier nonterminal symbol. -
When processing
strict mode code , an implementation must not relax theearly error rules of12.9.3.1 . -
TemplateEscapeSequence must not be extended to includeLegacyOctalEscapeSequence orNonOctalDecimalEscapeSequence as defined in12.9.4 . -
When processing
strict mode code , the extensions defined inB.3.1 ,B.3.2 ,B.3.3 , andB.3.5 must not be supported. -
When parsing for the
Module goal symbol , the lexical grammar extensions defined inB.1.1 must not be supported. -
ImportCall must not be extended.
18 ECMAScript Standard Built-in Objects
There are certain built-in objects available whenever an ECMAScript
Unless specified otherwise, a built-in object that is callable as a function is a built-in
Many built-in objects are functions: they can be invoked with arguments. Some of them furthermore are
new operator. For each built-in function, this specification describes the
arguments required by that function and the properties of that new expression that invokes that
Unless otherwise specified in the description of a particular function, if a built-in function or
Unless otherwise specified in the description of a particular function, if a built-in function or
Implementations that add additional capabilities to the set of built-in functions are encouraged to do so by adding new functions rather than adding new parameters to existing functions.
Unless otherwise specified every built-in function and every built-in Function.prototype
(
Unless otherwise specified every built-in prototype object has the Object.prototype
(
If this specification defines a built-in
Built-in
Built-in
Each built-in function defined in this specification is created by calling the
Every built-in
For example, the
Unless otherwise specified, the
Every built-in
The value of the
Unless otherwise specified, the
Every other
Every
19 The Global Object
The global object:
- is created before control enters any
execution context . - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a [[Call]] internal method; it cannot be invoked as a function.
- has a [[Prototype]] internal slot whose value is
host-defined . - may have
host-defined properties in addition to the properties defined in this specification. This may include a property whose value is the global object itself.
19.1 Value Properties of the Global Object
19.1.1 globalThis
The initial value of the
This property has the attributes { [[Writable]]:
19.1.2 Infinity
The value of Infinity is
19.1.3 NaN
The value of NaN is
19.1.4 undefined
The value of undefined is
19.2 Function Properties of the Global Object
19.2.1 eval ( x )
This function is the %eval% intrinsic object.
It performs the following steps when called:
- Return ?
PerformEval (x,false ,false ).
19.2.1.1 PerformEval ( x, strictCaller, direct )
The abstract operation PerformEval takes arguments x (an
Assert : If direct isfalse , then strictCaller is alsofalse .- If x
is not a String , return x. - Let evalRealm be
the current Realm Record . - NOTE: In the case of a
direct eval , evalRealm is therealm of both the caller ofevaland of theevalfunction itself. - Perform ?
HostEnsureCanCompileStrings (evalRealm, « », x, direct). - Let inFunction be
false . - Let inMethod be
false . - Let inDerivedConstructor be
false . - Let inClassFieldInitializer be
false . - If direct is
true , then- Let thisEnvRec be
GetThisEnvironment (). - If thisEnvRec is a
Function Environment Record , then- Let F be thisEnvRec.[[FunctionObject]].
- Set inFunction to
true . - Set inMethod to thisEnvRec.HasSuperBinding().
- If F.[[ConstructorKind]] is
derived , set inDerivedConstructor totrue . - Let classFieldInitializerName be F.[[ClassFieldInitializerName]].
- If classFieldInitializerName is not
empty , set inClassFieldInitializer totrue .
- Let thisEnvRec be
- Perform the following substeps in an
implementation-defined order, possibly interleaving parsing and error detection:- Let script be
ParseText (StringToCodePoints (x),Script ). - If script is a
List of errors, throw aSyntaxError exception. - If script
Contains ScriptBody isfalse , returnundefined . - Let body be the
ScriptBody of script. - If inFunction is
false and bodyContains NewTarget , throw aSyntaxError exception. - If inMethod is
false and bodyContains SuperProperty , throw aSyntaxError exception. - If inDerivedConstructor is
false and bodyContains SuperCall , throw aSyntaxError exception. - If inClassFieldInitializer is
true andContainsArguments of body istrue , throw aSyntaxError exception.
- Let script be
- If strictCaller is
true , let strictEval betrue . - Else, let strictEval be
IsStrict of script. - Let runningContext be the
running execution context . - NOTE: If direct is
true , runningContext will be theexecution context that performed thedirect eval . If direct isfalse , runningContext will be theexecution context for the invocation of theevalfunction. - If direct is
true , then- Let lexEnv be
NewDeclarativeEnvironment (runningContext's LexicalEnvironment). - Let varEnv be runningContext's VariableEnvironment.
- Let privateEnv be runningContext's PrivateEnvironment.
- Let lexEnv be
- Else,
- Let lexEnv be
NewDeclarativeEnvironment (evalRealm.[[GlobalEnv]]). - Let varEnv be evalRealm.[[GlobalEnv]].
- Let privateEnv be
null .
- Let lexEnv be
- If strictEval is
true , set varEnv to lexEnv. - If runningContext is not already suspended, suspend runningContext.
- Let evalContext be a new
ECMAScript code execution context . - Set evalContext's Function to
null . - Set evalContext's
Realm to evalRealm. - Set evalContext's ScriptOrModule to runningContext's ScriptOrModule.
- Set evalContext's VariableEnvironment to varEnv.
- Set evalContext's LexicalEnvironment to lexEnv.
- Set evalContext's PrivateEnvironment to privateEnv.
- Push evalContext onto the
execution context stack ; evalContext is now therunning execution context . - Let result be
Completion (EvalDeclarationInstantiation (body, varEnv, lexEnv, privateEnv, strictEval)). - If result is a
normal completion , then- Set result to
Completion (Evaluation of body).
- Set result to
- If result is a
normal completion and result.[[Value]] isempty , then- Set result to
NormalCompletion (undefined ).
- Set result to
- Suspend evalContext and remove it from the
execution context stack . - Resume the context that is now on the top of the
execution context stack as therunning execution context . - Return ? result.
The eval code cannot instantiate variable or function bindings in the variable environment of the
calling context that invoked the eval if either the code of the calling context or the eval code
is
let, const, or class declarations
are
always instantiated in a new LexicalEnvironment.
19.2.1.2 HostEnsureCanCompileStrings ( calleeRealm, parameterStrings, bodyString, direct )
The
parameterStrings represents the strings that, when using one of the function eval call.
direct signifies whether the evaluation is a
The default implementation of HostEnsureCanCompileStrings is to return
19.2.1.3 EvalDeclarationInstantiation ( body, varEnv, lexEnv, privateEnv, strict )
The abstract operation EvalDeclarationInstantiation takes arguments body (a
- Let varNames be the
VarDeclaredNames of body. - Let varDeclarations be the
VarScopedDeclarations of body. - If strict is
false , then- If varEnv is a
Global Environment Record , then- For each element name of
varNames,
do
- If
varEnv.HasLexicalDeclaration(name) is
true , throw aSyntaxError exception. - NOTE:
evalwill not create a global var declaration that would be shadowed by a global lexical declaration.
- If
varEnv.HasLexicalDeclaration(name) is
- For each element name of
varNames,
do
- Let thisEnv be lexEnv.
Assert : The following loop will terminate.- Repeat, while thisEnv is not
varEnv,
- If thisEnv
is not an Object Environment Record , then- NOTE: The environment of with statements cannot contain any lexical declaration so it doesn't need to be checked for var/let hoisting conflicts.
- For each element name of
varNames, do
- If
! thisEnv.HasBinding(name) is
true , then- Throw a
SyntaxError exception. - NOTE: Annex
B.3.4 defines alternate semantics for the above step.
- Throw a
- NOTE: A
direct eval will not hoist var declaration over a like-named lexical declaration.
- If
! thisEnv.HasBinding(name) is
- Set thisEnv to thisEnv.[[OuterEnv]].
- If thisEnv
- If varEnv is a
- Let privateIdentifiers be a new empty
List . - Let pointer be privateEnv.
- Repeat, while pointer is not
null ,- For each
Private Name binding of pointer.[[Names]], do- If privateIdentifiers does not contain binding.[[Description]], append binding.[[Description]] to privateIdentifiers.
- Set pointer to pointer.[[OuterPrivateEnvironment]].
- For each
- If
AllPrivateIdentifiersValid of body with argument privateIdentifiers isfalse , throw aSyntaxError exception. - Let functionsToInitialize be a new empty
List . - Let declaredFunctionNames be a new empty
List . - For each element d of varDeclarations,
in
reverse
List order, do- If d is not either a
VariableDeclaration , aForBinding , or aBindingIdentifier , thenAssert : d is either aFunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration .- NOTE: If there are multiple function declarations for the same name, the last declaration is used.
- Let fn be the sole element of the
BoundNames of d. - If declaredFunctionNames does not contain
fn, then
- If varEnv is a
Global Environment Record , then- Let fnDefinable be ? varEnv.CanDeclareGlobalFunction(fn).
- If fnDefinable is
false , throw aTypeError exception.
- Append fn to declaredFunctionNames.
- Insert d as the first element of functionsToInitialize.
- If varEnv is a
- If d is not either a
- Let declaredVarNames be a new empty
List . - For each element d of varDeclarations,
do
- If d is either a
VariableDeclaration , aForBinding , or aBindingIdentifier , then- For each String vn of the
BoundNames of d, do- If declaredFunctionNames does not
contain
vn, then
- If varEnv is a
Global Environment Record , then- Let vnDefinable be ? varEnv.CanDeclareGlobalVar(vn).
- If vnDefinable is
false , throw aTypeError exception.
- If declaredVarNames does not
contain
vn, then
- Append vn to declaredVarNames.
- If varEnv is a
- If declaredFunctionNames does not
contain
vn, then
- For each String vn of the
- If d is either a
- NOTE: Annex
B.3.2.3 adds additional steps at this point. - NOTE:
No
abnormal terminations occur after this algorithm step unless varEnv is a
Global Environment Record and theglobal object is aProxy exotic object . - Let lexDeclarations be the
LexicallyScopedDeclarations of body. - For each element d of lexDeclarations,
do
- NOTE: Lexically declared names are only instantiated here but not initialized.
- For each element dn of the
BoundNames of d, do- If
IsConstantDeclaration of d istrue , then- Perform
? lexEnv.CreateImmutableBinding(dn,
true ).
- Perform
? lexEnv.CreateImmutableBinding(dn,
- Else,
- Perform
? lexEnv.CreateMutableBinding(dn,
false ).
- Perform
? lexEnv.CreateMutableBinding(dn,
- If
- For each
Parse Node f of functionsToInitialize, do- Let fn be the sole element of the
BoundNames of f. - Let fo be
InstantiateFunctionObject of f with arguments lexEnv and privateEnv. - If varEnv is a
Global Environment Record , then- Perform
? varEnv.CreateGlobalFunctionBinding(fn, fo,
true ).
- Perform
? varEnv.CreateGlobalFunctionBinding(fn, fo,
- Else,
- Let bindingExists be ! varEnv.HasBinding(fn).
- If bindingExists is
false , then- NOTE: The following invocation cannot return an
abrupt completion because of the validation preceding step14 . - Perform
! varEnv.CreateMutableBinding(fn,
true ). - Perform ! varEnv.InitializeBinding(fn, fo).
- NOTE: The following invocation cannot return an
- Else,
- Perform
! varEnv.SetMutableBinding(fn, fo,
false ).
- Perform
! varEnv.SetMutableBinding(fn, fo,
- Let fn be the sole element of the
- For each String vn of
declaredVarNames,
do
- If varEnv is a
Global Environment Record , then- Perform
? varEnv.CreateGlobalVarBinding(vn,
true ).
- Perform
? varEnv.CreateGlobalVarBinding(vn,
- Else,
- Let bindingExists be ! varEnv.HasBinding(vn).
- If bindingExists is
false , then- NOTE: The following invocation cannot return an
abrupt completion because of the validation preceding step14 . - Perform
! varEnv.CreateMutableBinding(vn,
true ). - Perform
! varEnv.InitializeBinding(vn,
undefined ).
- NOTE: The following invocation cannot return an
- If varEnv is a
- Return
unused .
An alternative version of this algorithm is described in
19.2.2 isFinite ( number )
This function is the %isFinite% intrinsic object.
It performs the following steps when called:
19.2.3 isNaN ( number )
This function is the %isNaN% intrinsic object.
It performs the following steps when called:
- Let num be ?
ToNumber (number). - If num is
NaN , returntrue . - Otherwise, return
false .
A reliable way for ECMAScript code to test if a value X is X !== X. The result will be X is
19.2.4 parseFloat ( string )
This function produces a Number value dictated by interpretation of the contents of the string argument as a decimal literal.
It is the %parseFloat% intrinsic object.
It performs the following steps when called:
- Let inputString be ?
ToString (string). - Let trimmedString be !
TrimString (inputString,start ). - Let trimmed be
StringToCodePoints (trimmedString). - Let trimmedPrefix be the longest prefix of
trimmed that satisfies the syntax of a
StrDecimalLiteral , which might be trimmed itself. If there is no such prefix, returnNaN . - Let parsedNumber be
ParseText (trimmedPrefix,StrDecimalLiteral ). Assert : parsedNumber is aParse Node .- Return
StringNumericValue of parsedNumber.
This function may interpret only a leading portion of string as a Number value; it ignores any code units that cannot be interpreted as part of the notation of a decimal literal, and no indication is given that any such code units were ignored.
19.2.5 parseInt ( string, radix )
This function produces an
It is the %parseInt% intrinsic object.
It performs the following steps when called:
- Let inputString be ?
ToString (string). - Let S be !
TrimString (inputString,start ). - Let sign be 1.
- If S is not empty and the first code unit of S is the code unit 0x002D (HYPHEN-MINUS), set sign to -1.
- If S is not empty and the first code unit of
S is either the code unit 0x002B (PLUS SIGN) or the code unit 0x002D (HYPHEN-MINUS), set
S to the
substring of S from index 1. - Let R be
ℝ (?ToInt32 (radix)). - Let stripPrefix be
true . - If R ≠ 0, then
- If R < 2 or R > 36, return
NaN . - If R ≠ 16, set stripPrefix to
false .
- If R < 2 or R > 36, return
- Else,
- Set R to 10.
- If stripPrefix is
true , then- If the length of S is at least 2 and the first
two
code units of S are either
"0x" or"0X" , then- Set S to the
substring of S from index 2. - Set R to 16.
- Set S to the
- If the length of S is at least 2 and the first
two
code units of S are either
- If S contains a code unit that is not a radix-R digit, let end be the index within S of the first such code unit; otherwise, let end be the length of S.
- Let Z be the
substring of S from 0 to end. - If Z is empty, return
NaN . - Let mathInt be the
integer value that is represented by Z in radix-R notation, using the letters A through Z and a through z for digits with values 10 through 35. (However, if R = 10 and Z contains more than 20 significant digits, every significant digit after the 20th may be replaced by a 0 digit, at the option of the implementation; and if R is not one of 2, 4, 8, 10, 16, or 32, then mathInt may be animplementation-approximated integer representing theinteger value denoted by Z in radix-R notation.) - If mathInt = 0, then
- If sign = -1, return
-0 𝔽. - Return
+0 𝔽.
- If sign = -1, return
- Return
𝔽 (sign × mathInt).
19.2.6 URI Handling Functions
Uniform Resource Identifiers, or URIs, are Strings that identify resources (e.g. web pages or files)
and
transport protocols by which to access them (e.g. HTTP or FTP) on the Internet. The ECMAScript language
itself does not provide any support for using URIs except for functions that encode and decode URIs as
described in this section. encodeURI and decodeURI are intended to work with
complete URIs; they assume that any reserved characters are intended to have special meaning (e.g., as
delimiters) and so are not encoded. encodeURIComponent and decodeURIComponent
are
intended to work with the individual components of a URI; they assume that any reserved characters
represent
text and must be encoded to avoid special meaning when the component is part of a complete URI.
The set of reserved characters is based upon RFC 2396 and does not reflect changes introduced by the more recent RFC 3986.
Many implementations of ECMAScript provide additional functions and methods that manipulate web pages; these functions are beyond the scope of this standard.
19.2.6.1 decodeURI ( encodedURI )
This function computes a new version of a URI in which each escape sequence and UTF-8 encoding of the
sort that might be introduced by the encodeURI function is replaced with the UTF-16
encoding
of the code point that it represents. Escape sequences that could not have been introduced by
encodeURI are not replaced.
It is the %decodeURI% intrinsic object.
It performs the following steps when called:
19.2.6.2 decodeURIComponent ( encodedURIComponent )
This function computes a new version of a URI in which each escape sequence and UTF-8 encoding of the
sort that might be introduced by the encodeURIComponent function is replaced with the
UTF-16
encoding of the code point that it represents.
It is the %decodeURIComponent% intrinsic object.
It performs the following steps when called:
19.2.6.3 encodeURI ( uri )
This function computes a new version of a UTF-16 encoded (
It is the %encodeURI% intrinsic object.
It performs the following steps when called:
19.2.6.4 encodeURIComponent ( uriComponent )
This function computes a new version of a UTF-16 encoded (
It is the %encodeURIComponent% intrinsic object.
It performs the following steps when called:
19.2.6.5 Encode ( string, extraUnescaped )
The abstract operation Encode takes arguments string (a String) and
extraUnescaped
(a String) and returns either a
- Let len be the length of string.
- Let R be the empty String.
- Let alwaysUnescaped be the
string-concatenation ofthe ASCII word characters and"-.!~*'()" . - Let unescapedSet be the
string-concatenation of alwaysUnescaped and extraUnescaped. - Let k be 0.
- Repeat, while k < len,
- Let C be the code unit at index k within string.
- If unescapedSet contains C, then
- Set k to k + 1.
- Set R to the
string-concatenation of R and C.
- Else,
- Let cp be
CodePointAt (string, k). - If cp.[[IsUnpairedSurrogate]] is
true , throw aURIError exception. - Set k to k + cp.[[CodeUnitCount]].
- Let Octets be the
List of octets resulting by applying the UTF-8 transformation to cp.[[CodePoint]]. - For each element octet of
Octets,
do
- Let hex be the String representation of octet, formatted as an uppercase hexadecimal number.
- Set R to the
string-concatenation of R,"%" , andStringPad (hex, 2,"0" ,start ).
- Let cp be
- Return R.
Because percent-encoding is used to represent individual octets, a single code point may be expressed as multiple consecutive escape sequences (one for each of its 8-bit UTF-8 code units).
19.2.6.6 Decode ( string, preserveEscapeSet )
The abstract operation Decode takes arguments string (a String) and
preserveEscapeSet (a String) and returns either a
- Let len be the length of string.
- Let R be the empty String.
- Let k be 0.
- Repeat, while k < len,
- Let C be the code unit at index k within string.
- Let S be C.
- If C is the code unit 0x0025 (PERCENT SIGN),
then
- If k + 3 > len, throw a
URIError exception. - Let escape be the
substring of string from k to k + 3. - Let B be
ParseHexOctet (string, k + 1). - If B is not an
integer , throw aURIError exception. - Set k to k + 2.
- Let n be the number of leading 1 bits in B.
- If n = 0, then
- Let asciiChar be the code unit whose numeric value is B.
- If preserveEscapeSet contains asciiChar, set S to escape. Otherwise, set S to asciiChar.
- Else,
- If n = 1 or n > 4, throw
a
URIError exception. - Let Octets be « B ».
- Let j be 1.
- Repeat, while j < n,
- Set k to k + 1.
- If k + 3 > len,
throw
a
URIError exception. - If the code unit at index k within
string is not the code unit 0x0025 (PERCENT SIGN), throw a
URIError exception. - Let continuationByte be
ParseHexOctet (string, k + 1). - If continuationByte is not an
integer , throw aURIError exception. - Append continuationByte to Octets.
- Set k to k + 2.
- Set j to j + 1.
Assert : The length of Octets is n.- If Octets does not contain a valid
UTF-8
encoding of a Unicode code point, throw a
URIError exception. - Let V be the code point obtained by
applying the UTF-8 transformation to Octets, that is, from a
List of octets into a 21-bit value. - Set S to
UTF16EncodeCodePoint (V).
- If n = 1 or n > 4, throw
a
- If k + 3 > len, throw a
- Set R to the
string-concatenation of R and S. - Set k to k + 1.
- Return R.
RFC 3629 prohibits the decoding of invalid UTF-8 octet sequences. For example, the invalid
sequence
0xC0 0x80 must not decode into the code unit 0x0000. Implementations of the Decode algorithm are
required to throw a
19.2.6.7 ParseHexOctet ( string, position )
The abstract operation ParseHexOctet takes arguments string (a String) and
position
(a non-negative
- Let len be the length of string.
Assert : position + 2 ≤ len.- Let hexDigits be the
substring of string from position to position + 2. - Let parseResult be
ParseText (StringToCodePoints (hexDigits),HexDigits ).[~Sep] - If parseResult is not a
Parse Node , return parseResult. - Let n be the MV of parseResult.
Assert : n is in theinclusive interval from 0 to 255.- Return n.
19.3 Constructor Properties of the Global Object
19.3.1 AggregateError ( . . . )
See
19.3.2 Array ( . . . )
See
19.3.3 ArrayBuffer ( . . . )
See
19.3.4 BigInt ( . . . )
See
19.3.5 BigInt64Array ( . . . )
See
19.3.6 BigUint64Array ( . . . )
See
19.3.7 Boolean ( . . . )
See
19.3.8 DataView ( . . . )
See
19.3.9 Date ( . . . )
See
19.3.10 Error ( . . . )
See
19.3.11 EvalError ( . . . )
See
19.3.12 FinalizationRegistry ( . . . )
See
19.3.13 Float32Array ( . . . )
See
19.3.14 Float64Array ( . . . )
See
19.3.15 Function ( . . . )
See
19.3.16 Int8Array ( . . . )
See
19.3.17 Int16Array ( . . . )
See
19.3.18 Int32Array ( . . . )
See
19.3.19 Map ( . . . )
See
19.3.20 Number ( . . . )
See
19.3.21 Object ( . . . )
See
19.3.22 Promise ( . . . )
See
19.3.23 Proxy ( . . . )
See
19.3.24 RangeError ( . . . )
See
19.3.25 ReferenceError ( . . . )
See
19.3.26 RegExp ( . . . )
See
19.3.27 Set ( . . . )
See
19.3.28 SharedArrayBuffer ( . . . )
See
19.3.29 String ( . . . )
See
19.3.30 Symbol ( . . . )
See
19.3.31 SyntaxError ( . . . )
See
19.3.32 TypeError ( . . . )
See
19.3.33 Uint8Array ( . . . )
See
19.3.34 Uint8ClampedArray ( . . . )
See
19.3.35 Uint16Array ( . . . )
See
19.3.36 Uint32Array ( . . . )
See
19.3.37 URIError ( . . . )
See
19.3.38 WeakMap ( . . . )
See
19.3.39 WeakRef ( . . . )
See
19.3.40 WeakSet ( . . . )
See
19.4 Other Properties of the Global Object
19.4.1 Atomics
See
19.4.2 JSON
See
19.4.3 Math
See
19.4.4 Reflect
See
20 Fundamental Objects
20.1 Object Objects
20.1.1 The Object Constructor
The Object
- is %Object%.
- is the initial value of the
"Object" property of theglobal object . - creates a new
ordinary object when called as aconstructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition.
20.1.1.1 Object ( [ value ] )
This function performs the following steps when called:
- If NewTarget is neither
undefined nor theactive function object , then- Return ?
OrdinaryCreateFromConstructor (NewTarget,"%Object.prototype%" ).
- Return ?
- If value is either
undefined ornull , returnOrdinaryObjectCreate (%Object.prototype% ). - Return !
ToObject (value).
20.1.2 Properties of the Object Constructor
The Object
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is1 𝔽. - has the following additional properties:
20.1.2.1 Object.assign ( target, ...sources )
This function copies the values of all of the enumerable own properties from one or more source objects to a target object.
It performs the following steps when called:
The
20.1.2.2 Object.create ( O, Properties )
This function creates a new object with a specified prototype.
It performs the following steps when called:
- If O
is not an Object and O is notnull , throw aTypeError exception. - Let obj be
OrdinaryObjectCreate (O). - If Properties is not
undefined , then- Return ?
ObjectDefineProperties (obj, Properties).
- Return ?
- Return obj.
20.1.2.3 Object.defineProperties ( O, Properties )
This function adds own properties and/or updates the attributes of existing own properties of an object.
It performs the following steps when called:
- If O
is not an Object , throw aTypeError exception. - Return ?
ObjectDefineProperties (O, Properties).
20.1.2.3.1 ObjectDefineProperties ( O, Properties )
The abstract operation ObjectDefineProperties takes arguments O (an Object) and
Properties (an
- Let props be ?
ToObject (Properties). - Let keys be ? props.[[OwnPropertyKeys]]().
- Let descriptors be a new empty
List . - For each element nextKey of keys, do
- Let propDesc be ? props.[[GetOwnProperty]](nextKey).
- If propDesc is not
undefined and propDesc.[[Enumerable]] istrue , then- Let descObj be ?
Get (props, nextKey). - Let desc be ?
ToPropertyDescriptor (descObj). - Append the
Record { [[Key]]: nextKey, [[Descriptor]]: desc } to descriptors.
- Let descObj be ?
- For each element property of
descriptors,
do
- Perform ?
DefinePropertyOrThrow (O, property.[[Key]], property.[[Descriptor]]).
- Perform ?
- Return O.
20.1.2.4 Object.defineProperty ( O, P, Attributes )
This function adds an own property and/or updates the attributes of an existing own property of an object.
It performs the following steps when called:
- If O
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (P). - Let desc be ?
ToPropertyDescriptor (Attributes). - Perform ?
DefinePropertyOrThrow (O, key, desc). - Return O.
20.1.2.5 Object.entries ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let entryList be ?
EnumerableOwnProperties (obj,key+value ). - Return
CreateArrayFromList (entryList).
20.1.2.6 Object.freeze ( O )
This function performs the following steps when called:
- If O
is not an Object , return O. - Let status be ?
SetIntegrityLevel (O,frozen ). - If status is
false , throw aTypeError exception. - Return O.
20.1.2.7 Object.fromEntries ( iterable )
This function performs the following steps when called:
- Perform ?
RequireObjectCoercible (iterable). - Let obj be
OrdinaryObjectCreate (%Object.prototype% ). Assert : obj is an extensibleordinary object with no own properties.- Let closure be a new
Abstract Closure with parameters (key, value) that captures obj and performs the following steps when called:- Let propertyKey be ?
ToPropertyKey (key). - Perform !
CreateDataPropertyOrThrow (obj, propertyKey, value). - Return
undefined .
- Let propertyKey be ?
- Let adder be
CreateBuiltinFunction (closure, 2,"" , « »). - Return ?
AddEntriesFromIterable (obj, iterable, adder).
20.1.2.8 Object.getOwnPropertyDescriptor ( O, P )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let key be ?
ToPropertyKey (P). - Let desc be ? obj.[[GetOwnProperty]](key).
- Return
FromPropertyDescriptor (desc).
20.1.2.9 Object.getOwnPropertyDescriptors ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let ownKeys be ? obj.[[OwnPropertyKeys]]().
- Let descriptors be
OrdinaryObjectCreate (%Object.prototype% ). - For each element key of ownKeys, do
- Let desc be ? obj.[[GetOwnProperty]](key).
- Let descriptor be
FromPropertyDescriptor (desc). - If descriptor is not
undefined , perform !CreateDataPropertyOrThrow (descriptors, key, descriptor).
- Return descriptors.
20.1.2.10 Object.getOwnPropertyNames ( O )
This function performs the following steps when called:
- Return
CreateArrayFromList (?GetOwnPropertyKeys (O,string )).
20.1.2.11 Object.getOwnPropertySymbols ( O )
This function performs the following steps when called:
- Return
CreateArrayFromList (?GetOwnPropertyKeys (O,symbol )).
20.1.2.11.1 GetOwnPropertyKeys ( O, type )
The abstract operation GetOwnPropertyKeys takes arguments O (an
- Let obj be ?
ToObject (O). - Let keys be ? obj.[[OwnPropertyKeys]]().
- Let nameList be a new empty
List . - For each element nextKey of keys, do
- If nextKey
is a Symbol and type issymbol , or if nextKeyis a String and type isstring , then- Append nextKey to nameList.
- If nextKey
- Return nameList.
20.1.2.12 Object.getPrototypeOf ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Return ? obj.[[GetPrototypeOf]]().
20.1.2.13 Object.groupBy ( items, callbackfn )
callbackfn should be a function that accepts two arguments. groupBy calls
callbackfn once for each element in items, in ascending order, and
constructs
a
new object. Each value returned by callbackfn is coerced to a
callbackfn is called with two arguments: the value of the element and the index of the element.
The return value of groupBy is an object that does not inherit from
This function performs the following steps when called:
- Let groups be ?
GroupBy (items, callbackfn,property ). - Let obj be
OrdinaryObjectCreate (null ). - For each
Record { [[Key]], [[Elements]] } g of groups, do- Let elements be
CreateArrayFromList (g.[[Elements]]). - Perform !
CreateDataPropertyOrThrow (obj, g.[[Key]], elements).
- Let elements be
- Return obj.
20.1.2.14 Object.hasOwn ( O, P )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let key be ?
ToPropertyKey (P). - Return ?
HasOwnProperty (obj, key).
20.1.2.15 Object.is ( value1, value2 )
This function performs the following steps when called:
- Return
SameValue (value1, value2).
20.1.2.16 Object.isExtensible ( O )
This function performs the following steps when called:
- If O
is not an Object , returnfalse . - Return ?
IsExtensible (O).
20.1.2.17 Object.isFrozen ( O )
This function performs the following steps when called:
- If O
is not an Object , returntrue . - Return ?
TestIntegrityLevel (O,frozen ).
20.1.2.18 Object.isSealed ( O )
This function performs the following steps when called:
- If O
is not an Object , returntrue . - Return ?
TestIntegrityLevel (O,sealed ).
20.1.2.19 Object.keys ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let keyList be ?
EnumerableOwnProperties (obj,key ). - Return
CreateArrayFromList (keyList).
20.1.2.20 Object.preventExtensions ( O )
This function performs the following steps when called:
- If O
is not an Object , return O. - Let status be ? O.[[PreventExtensions]]().
- If status is
false , throw aTypeError exception. - Return O.
20.1.2.21 Object.prototype
The initial value of Object.prototype is the
This property has the attributes { [[Writable]]:
20.1.2.22 Object.seal ( O )
This function performs the following steps when called:
- If O
is not an Object , return O. - Let status be ?
SetIntegrityLevel (O,sealed ). - If status is
false , throw aTypeError exception. - Return O.
20.1.2.23 Object.setPrototypeOf ( O, proto )
This function performs the following steps when called:
- Set O to ?
RequireObjectCoercible (O). - If proto
is not an Object and proto is notnull , throw aTypeError exception. - If O
is not an Object , return O. - Let status be ? O.[[SetPrototypeOf]](proto).
- If status is
false , throw aTypeError exception. - Return O.
20.1.2.24 Object.values ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let valueList be ?
EnumerableOwnProperties (obj,value ). - Return
CreateArrayFromList (valueList).
20.1.3 Properties of the Object Prototype Object
The Object prototype object:
- is %Object.prototype%.
- has an [[Extensible]] internal slot whose value is
true . - has the internal methods defined for
ordinary objects , except for the [[SetPrototypeOf]] method, which is as defined in10.4.7.1 . (Thus, it is animmutable prototype exotic object .) - has a [[Prototype]] internal slot whose value is
null .
20.1.3.1 Object.prototype.constructor
The initial value of Object.prototype.constructor is
20.1.3.2 Object.prototype.hasOwnProperty ( V )
This method performs the following steps when called:
- Let P be
?
ToPropertyKey (V). - Let O be
?
ToObject (this value). - Return ?
HasOwnProperty (O, P).
20.1.3.3 Object.prototype.isPrototypeOf ( V )
This method performs the following steps when called:
- If V
is not an Object , returnfalse . - Let O be
?
ToObject (this value). - Repeat,
- Set V to ? V.[[GetPrototypeOf]]().
- If V is
null , returnfalse . - If
SameValue (O, V) istrue , returntrue .
20.1.3.4 Object.prototype.propertyIsEnumerable ( V )
This method performs the following steps when called:
- Let P
be
?
ToPropertyKey (V). - Let O be
?
ToObject (this value). - Let desc be ? O.[[GetOwnProperty]](P).
- If desc is
undefined , returnfalse . - Return desc.[[Enumerable]].
This method does not consider objects in the prototype chain.
20.1.3.5 Object.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
This method performs the following steps when called:
- Let O be the
this value. - Return ?
Invoke (O,"toString" ).
The optional parameters to this method are not used but are intended to correspond to the parameter
pattern used by ECMA-402 toLocaleString methods. Implementations that do not include
ECMA-402
support must not use those parameter positions for other purposes.
This method provides a generic toLocaleString implementation for objects that have
no
locale-sensitive toString behaviour. Array, Number,
Date, and toLocaleString methods.
ECMA-402 intentionally does not provide an alternative to this default implementation.
20.1.3.6 Object.prototype.toString ( )
This method performs the following steps when called:
- If the
this value isundefined , return"[object Undefined]" . - If the
this value isnull , return"[object Null]" . - Let O be !
ToObject (this value). - Let isArray be ?
IsArray (O). - If isArray is
true , let builtinTag be"Array" . - Else if O has a [[ParameterMap]] internal slot, let builtinTag be
"Arguments" . - Else if O has a [[Call]]
internal method, let builtinTag be
"Function" . - Else if O has an [[ErrorData]] internal slot, let builtinTag be
"Error" . - Else if O has a [[BooleanData]] internal slot, let builtinTag be
"Boolean" . - Else if O has a [[NumberData]] internal slot, let builtinTag be
"Number" . - Else if O has a [[StringData]] internal slot, let builtinTag be
"String" . - Else if O has a [[DateValue]] internal slot, let builtinTag be
"Date" . - Else if O has a [[RegExpMatcher]] internal slot, let builtinTag be
"RegExp" . - Else, let builtinTag be
"Object" . - Let tag be ?
Get (O,@@toStringTag ). - If tag
is not a String , set tag to builtinTag. - Return the
string-concatenation of"[object " , tag, and"]" .
Historically, this method was occasionally used to access the String value of the [[Class]] internal slot that was used in previous editions of this
specification
as a nominal type tag for various built-in objects. The above definition of toString
preserves compatibility for legacy code that uses toString as a test for those
specific
kinds of built-in objects. It does not provide a reliable type testing mechanism for other kinds
of
built-in or program defined objects. In addition, programs can use
20.1.3.7 Object.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ToObject (this value).
20.1.3.8 Object.prototype.__proto__
Object.prototype.__proto__ is an
20.1.3.8.1 get Object.prototype.__proto__
The value of the [[Get]] attribute is a built-in function that requires no arguments. It performs the following steps when called:
- Let O be ?
ToObject (this value). - Return ? O.[[GetPrototypeOf]]().
20.1.3.8.2 set Object.prototype.__proto__
The value of the [[Set]] attribute is a built-in function that takes an argument proto. It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If proto
is not an Object and proto is notnull , returnundefined . - If O
is not an Object , returnundefined . - Let status be ? O.[[SetPrototypeOf]](proto).
- If status is
false , throw aTypeError exception. - Return
undefined .
20.1.3.9 Legacy Object.prototype Accessor Methods
20.1.3.9.1 Object.prototype.__defineGetter__ ( P, getter )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - If
IsCallable (getter) isfalse , throw aTypeError exception. - Let desc be PropertyDescriptor { [[Get]]: getter, [[Enumerable]]:
true , [[Configurable]]:true }. - Let key be ?
ToPropertyKey (P). - Perform ?
DefinePropertyOrThrow (O, key, desc). - Return
undefined .
20.1.3.9.2 Object.prototype.__defineSetter__ ( P, setter )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - If
IsCallable (setter) isfalse , throw aTypeError exception. - Let desc be PropertyDescriptor { [[Set]]: setter, [[Enumerable]]:
true , [[Configurable]]:true }. - Let key be ?
ToPropertyKey (P). - Perform ?
DefinePropertyOrThrow (O, key, desc). - Return
undefined .
20.1.3.9.3 Object.prototype.__lookupGetter__ ( P )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let key be ?
ToPropertyKey (P). - Repeat,
- Let desc be ? O.[[GetOwnProperty]](key).
- If desc is not
undefined , then- If
IsAccessorDescriptor (desc) istrue , return desc.[[Get]]. - Return
undefined .
- If
- Set O to ? O.[[GetPrototypeOf]]().
- If O is
null , returnundefined .
20.1.3.9.4 Object.prototype.__lookupSetter__ ( P )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let key be ?
ToPropertyKey (P). - Repeat,
- Let desc be ? O.[[GetOwnProperty]](key).
- If desc is not
undefined , then- If
IsAccessorDescriptor (desc) istrue , return desc.[[Set]]. - Return
undefined .
- If
- Set O to ? O.[[GetPrototypeOf]]().
- If O is
null , returnundefined .
20.1.4 Properties of Object Instances
Object instances have no special properties beyond those inherited from the
20.2 Function Objects
20.2.1 The Function Constructor
The Function
- is %Function%.
- is the initial value of the
"Function" property of theglobal object . - creates and initializes a new
function object when called as a function rather than as aconstructor . Thus the function callFunction(…)is equivalent to the object creation expressionnew Function(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Function behaviour must include asupercall to the Functionconstructor to create and initialize a subclass instance with the internal slots necessary for built-in function behaviour. All ECMAScript syntactic forms for definingfunction objects create instances of Function. There is no syntactic means to create instances of Function subclasses except for the built-in GeneratorFunction, AsyncFunction, and AsyncGeneratorFunction subclasses.
20.2.1.1 Function ( ...parameterArgs, bodyArg )
The last argument (if any) specifies the body (executable code) of a function; any preceding arguments specify formal parameters.
This function performs the following steps when called:
- Let C be the
active function object . - If bodyArg is not present, set bodyArg to the empty String.
- Return ?
CreateDynamicFunction (C, NewTarget,normal , parameterArgs, bodyArg).
It is permissible but not necessary to have one argument for each formal parameter to be specified. For example, all three of the following expressions produce the same result:
new Function("a", "b", "c", "return a+b+c")
new Function("a, b, c", "return a+b+c")
new Function("a,b", "c", "return a+b+c")20.2.1.1.1 CreateDynamicFunction ( constructor, newTarget, kind, parameterArgs, bodyArg )
The abstract operation CreateDynamicFunction takes arguments constructor (a new was initially applied to. parameterArgs and bodyArg reflect
the
argument values that were passed to constructor. It performs the following steps when
called:
- If newTarget is
undefined , set newTarget to constructor. - If kind is
normal , then- Let prefix be
"function" . - Let exprSym be the grammar symbol
FunctionExpression . - Let bodySym be the grammar symbol
FunctionBody .[~Yield, ~Await] - Let parameterSym be the grammar symbol
FormalParameters .[~Yield, ~Await] - Let fallbackProto be
"%Function.prototype%" .
- Let prefix be
- Else if kind is
generator , then- Let prefix be
"function*" . - Let exprSym be the grammar symbol
GeneratorExpression . - Let bodySym be the grammar symbol
GeneratorBody . - Let parameterSym be the grammar symbol
FormalParameters .[+Yield, ~Await] - Let fallbackProto be
"%GeneratorFunction.prototype%" .
- Let prefix be
- Else if kind is
async , then- Let prefix be
"async function" . - Let exprSym be the grammar symbol
AsyncFunctionExpression . - Let bodySym be the grammar symbol
AsyncFunctionBody . - Let parameterSym be the grammar symbol
FormalParameters .[~Yield, +Await] - Let fallbackProto be
"%AsyncFunction.prototype%" .
- Let prefix be
- Else,
Assert : kind isasync-generator .- Let prefix be
"async function*" . - Let exprSym be the grammar symbol
AsyncGeneratorExpression . - Let bodySym be the grammar symbol
AsyncGeneratorBody . - Let parameterSym be the grammar symbol
FormalParameters .[+Yield, +Await] - Let fallbackProto be
"%AsyncGeneratorFunction.prototype%" .
- Let argCount be the number of elements in parameterArgs.
- Let bodyString be ?
ToString (bodyArg). - Let parameterStrings be a new empty
List . - For each element arg of
parameterArgs,
do
- Append ?
ToString (arg) to parameterStrings.
- Append ?
- Let currentRealm be
the current Realm Record . - Perform ?
HostEnsureCanCompileStrings (currentRealm, parameterStrings, bodyString,false ). - Let P be the empty String.
- If argCount > 0, then
- Set P to parameterStrings[0].
- Let k be 1.
- Repeat, while k < argCount,
- Let nextArgString be parameterStrings[k].
- Set P to the
string-concatenation of P,"," (a comma), and nextArgString. - Set k to k + 1.
- Let bodyParseString be the
string-concatenation of 0x000A (LINE FEED), bodyString, and 0x000A (LINE FEED). - Let sourceString be the
string-concatenation of prefix," anonymous(" , P, 0x000A (LINE FEED),") {" , bodyParseString, and"}" . - Let sourceText be
StringToCodePoints (sourceString). - Let parameters be
ParseText (StringToCodePoints (P), parameterSym). - If parameters is a
List of errors, throw aSyntaxError exception. - Let body be
ParseText (StringToCodePoints (bodyParseString), bodySym). - If body is a
List of errors, throw aSyntaxError exception. - NOTE: The parameters and body are parsed separately to
ensure
that each is valid alone. For example,
new Function("/*", "*/ ) {")does not evaluate to a function. - NOTE: If this step is reached, sourceText must have the syntax of exprSym (although the reverse implication does not hold). The purpose of the next two steps is to enforce any Early Error rules which apply to exprSym directly.
- Let expr be
ParseText (sourceText, exprSym). - If expr is a
List of errors, throw aSyntaxError exception. - Let proto be ?
GetPrototypeFromConstructor (newTarget, fallbackProto). - Let env be currentRealm.[[GlobalEnv]].
- Let privateEnv be
null . - Let F be
OrdinaryFunctionCreate (proto, sourceText, parameters, body,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F,"anonymous" ). - If kind is
generator , then- Let prototype be
OrdinaryObjectCreate (%GeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }).
- Let prototype be
- Else if kind is
async-generator , then- Let prototype be
OrdinaryObjectCreate (%AsyncGeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }).
- Let prototype be
- Else if kind is
normal , then- Perform
MakeConstructor (F).
- Perform
- NOTE: Functions whose kind is
async are not constructible and do not have a [[Construct]] internal method or a"prototype" property. - Return F.
CreateDynamicFunction defines a
20.2.2 Properties of the Function Constructor
The Function
- is itself a built-in
function object . - has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is1 𝔽. - has the following properties:
20.2.2.1 Function.prototype
The value of Function.prototype is the
This property has the attributes { [[Writable]]:
20.2.3 Properties of the Function Prototype Object
The Function prototype object:
- is %Function.prototype%.
- is itself a built-in
function object . - accepts any arguments and returns
undefined when invoked. - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - has a [[Prototype]] internal slot whose value is
%Object.prototype% . - does not have a
"prototype" property. - has a
"length" property whose value is+0 𝔽. - has a
"name" property whose value is the empty String.
The Function prototype object is specified to be a
20.2.3.1 Function.prototype.apply ( thisArg, argArray )
This method performs the following steps when called:
- Let func be the
this value. - If
IsCallable (func) isfalse , throw aTypeError exception. - If argArray is either
undefined ornull , then- Perform
PrepareForTailCall (). - Return ?
Call (func, thisArg).
- Perform
- Let argList be ?
CreateListFromArrayLike (argArray). - Perform
PrepareForTailCall (). - Return ?
Call (func, thisArg, argList).
The thisArg value is passed without modification as the
If func is either an arrow function or a
20.2.3.2 Function.prototype.bind ( thisArg, ...args )
This method performs the following steps when called:
- Let Target be the
this value. - If
IsCallable (Target) isfalse , throw aTypeError exception. - Let F be ?
BoundFunctionCreate (Target, thisArg, args). - Let L be 0.
- Let targetHasLength be ?
HasOwnProperty (Target,"length" ). - If targetHasLength is
true , then- Let targetLen be ?
Get (Target,"length" ). - If targetLen
is a Number , then- If targetLen is
+∞ 𝔽, then- Set L to +∞.
- Else if targetLen is
-∞ 𝔽, then- Set L to 0.
- Else,
- Let targetLenAsInt be !
ToIntegerOrInfinity (targetLen). Assert : targetLenAsInt isfinite .- Let argCount be the number of elements in args.
- Set L to
max (targetLenAsInt - argCount, 0).
- Let targetLenAsInt be !
- If targetLen is
- Let targetLen be ?
- Perform
SetFunctionLength (F, L). - Let targetName be ?
Get (Target,"name" ). - If targetName
is not a String , set targetName to the empty String. - Perform
SetFunctionName (F, targetName,"bound" ). - Return F.
Function.prototype.bind are
If Target is either an arrow function or a
20.2.3.3 Function.prototype.call ( thisArg, ...args )
This method performs the following steps when called:
- Let func be the
this value. - If
IsCallable (func) isfalse , throw aTypeError exception. - Perform
PrepareForTailCall (). - Return ?
Call (func, thisArg, args).
The thisArg value is passed without modification as the
If func is either an arrow function or a
20.2.3.4 Function.prototype.constructor
The initial value of Function.prototype.constructor is
20.2.3.5 Function.prototype.toString ( )
This method performs the following steps when called:
- Let func be the
this value. - If func
is an Object , func has a [[SourceText]] internal slot, func.[[SourceText]] is a sequence of Unicode code points, andHostHasSourceTextAvailable (func) istrue , then- Return
CodePointsToString (func.[[SourceText]]).
- Return
- If func is a
built-in function object , return animplementation-defined String source code representation of func. The representation must have the syntax of aNativeFunction . Additionally, if func has an [[InitialName]] internal slot and func.[[InitialName]]is a String , the portion of the returned String that would be matched byNativeFunctionAccessor opt PropertyName must be the value of func.[[InitialName]]. - If func
is an Object andIsCallable (func) istrue , return animplementation-defined String source code representation of func. The representation must have the syntax of aNativeFunction . - Throw a
TypeError exception.
20.2.3.6 Function.prototype [ @@hasInstance ] ( V )
This method performs the following steps when called:
- Let F be the
this value. - Return ?
OrdinaryHasInstance (F, V).
This property has the attributes { [[Writable]]:
This is the default implementation of @@hasInstance that most functions inherit.
@@hasInstance is called by the instanceof operator to determine whether
a
value is an instance of a specific
v instanceof Fevaluates as
F[@@hasInstance](v)A instanceof by exposing a different
@@hasInstance method on the function.
This property is non-writable and non-configurable to prevent tampering that could be used to globally expose the target function of a bound function.
The value of the
20.2.4 Function Instances
Every Function instance is an ECMAScript Function.prototype.bind method (
Function instances have the following properties:
20.2.4.1 length
The value of the
20.2.4.2 name
The value of the
Anonymous functions objects that do not have a contextual name associated with them by this
specification
use the empty String as the value of the
20.2.4.3 prototype
Function instances that can be used as a
This property has the attributes { [[Writable]]:
Function.prototype.bind, or by evaluating a
20.2.5 HostHasSourceTextAvailable ( func )
The
An implementation of HostHasSourceTextAvailable must conform to the following requirements:
- It must be deterministic with respect to its parameters. Each time it is called with a specific func as its argument, it must return the same result.
The default implementation of HostHasSourceTextAvailable is to return
20.3 Boolean Objects
20.3.1 The Boolean Constructor
The Boolean
- is %Boolean%.
- is the initial value of the
"Boolean" property of theglobal object . - creates and initializes a new Boolean object when called as a
constructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Boolean behaviour must include asupercall to the Booleanconstructor to create and initialize the subclass instance with a [[BooleanData]] internal slot.
20.3.1.1 Boolean ( value )
This function performs the following steps when called:
- Let b be
ToBoolean (value). - If NewTarget is
undefined , return b. - Let O be ?
OrdinaryCreateFromConstructor (NewTarget,"%Boolean.prototype%" , « [[BooleanData]] »). - Set O.[[BooleanData]] to b.
- Return O.
20.3.2 Properties of the Boolean Constructor
The Boolean
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
20.3.2.1 Boolean.prototype
The initial value of Boolean.prototype is the
This property has the attributes { [[Writable]]:
20.3.3 Properties of the Boolean Prototype Object
The Boolean prototype object:
- is %Boolean.prototype%.
- is an
ordinary object . - is itself a Boolean object; it has a [[BooleanData]] internal slot with the
value
false . - has a [[Prototype]] internal slot whose value is
%Object.prototype% .
20.3.3.1 Boolean.prototype.constructor
The initial value of Boolean.prototype.constructor is
20.3.3.2 Boolean.prototype.toString ( )
This method performs the following steps when called:
- Let b be ?
ThisBooleanValue (this value). - If b is
true , return"true" ; else return"false" .
20.3.3.3 Boolean.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ThisBooleanValue (this value).
20.3.3.3.1 ThisBooleanValue ( value )
The abstract operation ThisBooleanValue takes argument value (an
- If value
is a Boolean , return value. - If value
is an Object and value has a [[BooleanData]] internal slot, then- Let b be value.[[BooleanData]].
Assert : bis a Boolean .- Return b.
- Throw a
TypeError exception.
20.3.4 Properties of Boolean Instances
Boolean instances are
20.4 Symbol Objects
20.4.1 The Symbol Constructor
The Symbol
- is %Symbol%.
- is the initial value of the
"Symbol" property of theglobal object . - returns a new Symbol value when called as a function.
- is not intended to be used with the
newoperator. - is not intended to be subclassed.
- may be used as the value of an
extendsclause of a class definition but asupercall to it will cause an exception.
20.4.1.1 Symbol ( [ description ] )
This function performs the following steps when called:
- If NewTarget is not
undefined , throw aTypeError exception. - If description is
undefined , let descString beundefined . - Else, let descString be ?
ToString (description). - Return a new Symbol whose [[Description]] is descString.
20.4.2 Properties of the Symbol Constructor
The Symbol
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
20.4.2.1 Symbol.asyncIterator
The initial value of Symbol.asyncIterator is the well known symbol
This property has the attributes { [[Writable]]:
20.4.2.2 Symbol.for ( key )
This function performs the following steps when called:
- Let stringKey be ?
ToString (key). - For each element e of the GlobalSymbolRegistry
List , do- If
SameValue (e.[[Key]], stringKey) istrue , return e.[[Symbol]].
- If
Assert : GlobalSymbolRegistry does not currently contain an entry for stringKey.- Let newSymbol be a new Symbol whose [[Description]] is stringKey.
- Append the
Record { [[Key]]: stringKey, [[Symbol]]: newSymbol } to the GlobalSymbolRegistryList . - Return newSymbol.
The GlobalSymbolRegistry is an append-only
20.4.2.3 Symbol.hasInstance
The initial value of Symbol.hasInstance is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.4 Symbol.isConcatSpreadable
The initial value of Symbol.isConcatSpreadable is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.5 Symbol.iterator
The initial value of Symbol.iterator is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.6 Symbol.keyFor ( sym )
This function performs the following steps when called:
- If sym
is not a Symbol , throw aTypeError exception. - Return
KeyForSymbol (sym).
20.4.2.7 Symbol.match
The initial value of Symbol.match is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.8 Symbol.matchAll
The initial value of Symbol.matchAll is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.9 Symbol.prototype
The initial value of Symbol.prototype is the
This property has the attributes { [[Writable]]:
20.4.2.10 Symbol.replace
The initial value of Symbol.replace is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.11 Symbol.search
The initial value of Symbol.search is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.12 Symbol.species
The initial value of Symbol.species is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.13 Symbol.split
The initial value of Symbol.split is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.14 Symbol.toPrimitive
The initial value of Symbol.toPrimitive is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.15 Symbol.toStringTag
The initial value of Symbol.toStringTag is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.16 Symbol.unscopables
The initial value of Symbol.unscopables is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.3 Properties of the Symbol Prototype Object
The Symbol prototype object:
- is %Symbol.prototype%.
- is an
ordinary object . is not a Symbol instance and does not have a [[SymbolData]] internal slot.- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
20.4.3.1 Symbol.prototype.constructor
The initial value of Symbol.prototype.constructor is
20.4.3.2 get Symbol.prototype.description
Symbol.prototype.description is an
- Let s be the
this value. - Let sym be ?
ThisSymbolValue (s). - Return sym.[[Description]].
20.4.3.3 Symbol.prototype.toString ( )
This method performs the following steps when called:
- Let sym be ?
ThisSymbolValue (this value). - Return
SymbolDescriptiveString (sym).
20.4.3.3.1 SymbolDescriptiveString ( sym )
The abstract operation SymbolDescriptiveString takes argument sym (a Symbol) and returns a String. It performs the following steps when called:
- Let desc be sym's [[Description]] value.
- If desc is
undefined , set desc to the empty String. Assert : descis a String .- Return the
string-concatenation of"Symbol(" , desc, and")" .
20.4.3.4 Symbol.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ThisSymbolValue (this value).
20.4.3.4.1 ThisSymbolValue ( value )
The abstract operation ThisSymbolValue takes argument value (an
- If value
is a Symbol , return value. - If value
is an Object and value has a [[SymbolData]] internal slot, then- Let s be value.[[SymbolData]].
Assert : sis a Symbol .- Return s.
- Throw a
TypeError exception.
20.4.3.5 Symbol.prototype [ @@toPrimitive ] ( hint )
This method is called by ECMAScript language operators to convert a Symbol object to a primitive value.
It performs the following steps when called:
- Return ?
ThisSymbolValue (this value).
The argument is ignored.
This property has the attributes { [[Writable]]:
The value of the
20.4.3.6 Symbol.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
20.4.4 Properties of Symbol Instances
Symbol instances are
20.4.5 Abstract Operations for Symbols
20.4.5.1 KeyForSymbol ( sym )
The abstract operation KeyForSymbol takes argument sym (a Symbol) and returns a String or
20.5 Error Objects
Instances of Error objects are thrown as exceptions when runtime errors occur. The Error objects may also serve as base objects for user-defined exception classes.
When an ECMAScript implementation detects a runtime error, it throws a new instance of one of the
NativeError objects defined in
20.5.1 The Error Constructor
The Error
- is %Error%.
- is the initial value of the
"Error" property of theglobal object . - creates and initializes a new Error object when called as a function rather than as a
constructor . Thus the function callError(…)is equivalent to the object creation expressionnew Error(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Error behaviour must include asupercall to the Errorconstructor to create and initialize subclass instances with an [[ErrorData]] internal slot.
20.5.1.1 Error ( message [ , options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , let newTarget be theactive function object ; else let newTarget be NewTarget. - Let O be ?
OrdinaryCreateFromConstructor (newTarget,"%Error.prototype%" , « [[ErrorData]] »). - If message is not
undefined , then- Let msg be ?
ToString (message). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"message" , msg).
- Let msg be ?
- Perform ?
InstallErrorCause (O, options). - Return O.
20.5.2 Properties of the Error Constructor
The Error
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
20.5.2.1 Error.prototype
The initial value of Error.prototype is the
This property has the attributes { [[Writable]]:
20.5.3 Properties of the Error Prototype Object
The Error prototype object:
- is %Error.prototype%.
- is an
ordinary object . - is not an Error instance and does not have an [[ErrorData]] internal slot.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
20.5.3.1 Error.prototype.constructor
The initial value of Error.prototype.constructor is
20.5.3.2 Error.prototype.message
The initial value of Error.prototype.message is the empty String.
20.5.3.3 Error.prototype.name
The initial value of Error.prototype.name is
20.5.3.4 Error.prototype.toString ( )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let name be ?
Get (O,"name" ). - If name is
undefined , set name to"Error" ; otherwise set name to ?ToString (name). - Let msg be ?
Get (O,"message" ). - If msg is
undefined , set msg to the empty String; otherwise set msg to ?ToString (msg). - If name is the empty String, return msg.
- If msg is the empty String, return name.
- Return the
string-concatenation of name, the code unit 0x003A (COLON), the code unit 0x0020 (SPACE), and msg.
20.5.4 Properties of Error Instances
Error instances are Object.prototype.toString.
20.5.5 Native Error Types Used in This Standard
A new instance of one of the NativeError objects below or of the AggregateError object is
thrown
when a runtime error is detected. All NativeError objects share the same structure, as
described
in
20.5.5.1 EvalError
The EvalError
This exception is not currently used within this specification. This object remains for compatibility with previous editions of this specification.
20.5.5.2 RangeError
The RangeError
Indicates a value that is not in the set or range of allowable values.
20.5.5.3 ReferenceError
The ReferenceError
Indicate that an invalid reference has been detected.
20.5.5.4 SyntaxError
The SyntaxError
Indicates that a parsing error has occurred.
20.5.5.5 TypeError
The TypeError
TypeError is used to indicate an unsuccessful operation when none of the other NativeError objects are an appropriate indication of the failure cause.
20.5.5.6 URIError
The URIError
Indicates that one of the global URI handling functions was used in a way that is incompatible with its definition.
20.5.6 NativeError Object Structure
When an ECMAScript implementation detects a runtime error, it throws a new instance of one of the
NativeError objects defined in
For each error object, references to NativeError in the definition should be replaced with
the
appropriate error object name from
20.5.6.1 The NativeError Constructors
Each NativeError
- creates and initializes a new NativeError object when called as a function rather than
as
a
constructor . A call of the object as a function is equivalent to calling it as aconstructor with the same arguments. Thus the function callNativeError(…)is equivalent to the object creation expressionnew NativeError(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified NativeError behaviour must include asupercall to the NativeErrorconstructor to create and initialize subclass instances with an [[ErrorData]] internal slot.
20.5.6.1.1 NativeError ( message [ , options ] )
Each NativeError function performs the following steps when called:
- If NewTarget is
undefined , let newTarget be theactive function object ; else let newTarget be NewTarget. - Let
O be ?
OrdinaryCreateFromConstructor (newTarget,"%NativeError.prototype%", « [[ErrorData]] »). - If message is not
undefined , then- Let msg be ?
ToString (message). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"message" , msg).
- Let msg be ?
- Perform ?
InstallErrorCause (O, options). - Return O.
The actual value of the string passed in step
20.5.6.2 Properties of the NativeError Constructors
Each NativeError
- has a [[Prototype]] internal slot whose value is
%Error% . - has a
"name" property whose value is the String value"NativeError" . - has the following properties:
20.5.6.2.1 NativeError.prototype
The initial value of NativeError.prototype is a NativeError
prototype object (
This property has the attributes { [[Writable]]:
20.5.6.3 Properties of the NativeError Prototype Objects
Each NativeError prototype object:
- is an
ordinary object . - is not an Error instance and does not have an [[ErrorData]] internal slot.
- has a [[Prototype]] internal slot whose value is
%Error.prototype% .
20.5.6.3.1 NativeError.prototype.constructor
The initial value of the
20.5.6.3.2 NativeError.prototype.message
The initial value of the
20.5.6.3.3 NativeError.prototype.name
The initial value of the
20.5.6.4 Properties of NativeError Instances
NativeError instances are Object.prototype.toString
(
20.5.7 AggregateError Objects
20.5.7.1 The AggregateError Constructor
The AggregateError
- is %AggregateError%.
- is the initial value of the
"AggregateError" property of theglobal object . - creates and initializes a new AggregateError object when called as a function rather than as a
constructor . Thus the function callAggregateError(…)is equivalent to the object creation expressionnew AggregateError(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified AggregateError behaviour must include asupercall to the AggregateErrorconstructor to create and initialize subclass instances with an [[ErrorData]] internal slot.
20.5.7.1.1 AggregateError ( errors, message [ , options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , let newTarget be theactive function object ; else let newTarget be NewTarget. - Let O be ?
OrdinaryCreateFromConstructor (newTarget,"%AggregateError.prototype%" , « [[ErrorData]] »). - If message is not
undefined , then- Let msg be ?
ToString (message). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"message" , msg).
- Let msg be ?
- Perform ?
InstallErrorCause (O, options). - Let errorsList be ?
IteratorToList (?GetIterator (errors,sync )). - Perform !
DefinePropertyOrThrow (O,"errors" , PropertyDescriptor { [[Configurable]]:true , [[Enumerable]]:false , [[Writable]]:true , [[Value]]:CreateArrayFromList (errorsList) }). - Return O.
20.5.7.2 Properties of the AggregateError Constructor
The AggregateError
- has a [[Prototype]] internal slot whose value is
%Error% . - has the following properties:
20.5.7.2.1 AggregateError.prototype
The initial value of AggregateError.prototype is
This property has the attributes { [[Writable]]:
20.5.7.3 Properties of the AggregateError Prototype Object
The AggregateError prototype object:
- is %AggregateError.prototype%.
- is an
ordinary object . - is not an Error instance or an AggregateError instance and does not have an [[ErrorData]] internal slot.
- has a [[Prototype]] internal slot whose value is
%Error.prototype% .
20.5.7.3.1 AggregateError.prototype.constructor
The initial value of AggregateError.prototype.constructor is
20.5.7.3.2 AggregateError.prototype.message
The initial value of AggregateError.prototype.message is the empty String.
20.5.7.3.3 AggregateError.prototype.name
The initial value of AggregateError.prototype.name is
20.5.7.4 Properties of AggregateError Instances
AggregateError instances are Object.prototype.toString (
20.5.8 Abstract Operations for Error Objects
20.5.8.1 InstallErrorCause ( O, options )
The abstract operation InstallErrorCause takes arguments O (an Object) and
options
(an
- If options
is an Object and ?HasProperty (options,"cause" ) istrue , then- Let cause be ?
Get (options,"cause" ). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"cause" , cause).
- Let cause be ?
- Return
unused .
21 Numbers and Dates
21.1 Number Objects
21.1.1 The Number Constructor
The Number
- is %Number%.
- is the initial value of the
"Number" property of theglobal object . - creates and initializes a new Number object when called as a
constructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Number behaviour must include asupercall to the Numberconstructor to create and initialize the subclass instance with a [[NumberData]] internal slot.
21.1.1.1 Number ( value )
This function performs the following steps when called:
- If value is present, then
- Let prim be ?
ToNumeric (value). - If prim
is a BigInt , let n be𝔽 (ℝ (prim)). - Otherwise, let n be prim.
- Let prim be ?
- Else,
- Let n be
+0 𝔽.
- Let n be
- If NewTarget is
undefined , return n. - Let O be ?
OrdinaryCreateFromConstructor (NewTarget,"%Number.prototype%" , « [[NumberData]] »). - Set O.[[NumberData]] to n.
- Return O.
21.1.2 Properties of the Number Constructor
The Number
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
21.1.2.1 Number.EPSILON
The value of Number.EPSILON is the
This property has the attributes { [[Writable]]:
21.1.2.2 Number.isFinite ( number )
This function performs the following steps when called:
- If number
is not a Number , returnfalse . - If number is not
finite , returnfalse . - Otherwise, return
true .
21.1.2.3 Number.isInteger ( number )
This function performs the following steps when called:
- Return
IsIntegralNumber (number).
21.1.2.4 Number.isNaN ( number )
This function performs the following steps when called:
- If number
is not a Number , returnfalse . - If number is
NaN , returntrue . - Otherwise, return
false .
This function differs from the global isNaN function (
21.1.2.5 Number.isSafeInteger ( number )
An
This function performs the following steps when called:
- If
IsIntegralNumber (number) istrue , then - Return
false .
21.1.2.6 Number.MAX_SAFE_INTEGER
Due to rounding behaviour necessitated by precision limitations of Number.MAX_SAFE_INTEGER is shared with at least one other 9007199254740992 and 9007199254740993 evaluate to the Number value
The value of Number.MAX_SAFE_INTEGER is
This property has the attributes { [[Writable]]:
21.1.2.7 Number.MAX_VALUE
The value of Number.MAX_VALUE is the largest positive
This property has the attributes { [[Writable]]:
21.1.2.8 Number.MIN_SAFE_INTEGER
Due to rounding behaviour necessitated by precision limitations of Number.MIN_SAFE_INTEGER is shared with at least one other -9007199254740992 and -9007199254740993 evaluate to the Number
value
The value of Number.MIN_SAFE_INTEGER is
This property has the attributes { [[Writable]]:
21.1.2.9 Number.MIN_VALUE
The value of Number.MIN_VALUE is the smallest positive value of the
In the Number.MIN_VALUE must be the smallest non-zero
positive value that can actually be represented by the implementation.
This property has the attributes { [[Writable]]:
21.1.2.10 Number.NaN
The value of Number.NaN is
This property has the attributes { [[Writable]]:
21.1.2.11 Number.NEGATIVE_INFINITY
The value of Number.NEGATIVE_INFINITY is
This property has the attributes { [[Writable]]:
21.1.2.12 Number.parseFloat ( string )
The initial value of the
21.1.2.13 Number.parseInt ( string, radix )
The initial value of the
21.1.2.14 Number.POSITIVE_INFINITY
The value of Number.POSITIVE_INFINITY is
This property has the attributes { [[Writable]]:
21.1.2.15 Number.prototype
The initial value of Number.prototype is the
This property has the attributes { [[Writable]]:
21.1.3 Properties of the Number Prototype Object
The Number prototype object:
- is %Number.prototype%.
- is an
ordinary object . - is itself a Number object; it has a [[NumberData]] internal slot with the
value
+0 𝔽. - has a [[Prototype]] internal slot whose value is
%Object.prototype% .
Unless explicitly stated otherwise, the methods of the Number prototype object defined below are not
generic and the
The phrase “this Number value” within the specification of a method refers to the result returned by
calling the abstract operation
21.1.3.1 Number.prototype.constructor
The initial value of Number.prototype.constructor is
21.1.3.2 Number.prototype.toExponential ( fractionDigits )
This method returns a String containing this Number value represented in decimal exponential notation
with one digit before the significand's decimal point and fractionDigits digits after the
significand's decimal point. If fractionDigits is
It performs the following steps when called:
- Let x be ?
ThisNumberValue (this value). - Let f be ?
ToIntegerOrInfinity (fractionDigits). Assert : If fractionDigits isundefined , then f is 0.- If x is not
finite , returnNumber::toString (x, 10). - If f < 0 or f > 100, throw a
RangeError exception. - Set x to
ℝ (x). - Let s be the empty String.
- If x < 0, then
- Set s to
"-" . - Set x to -x.
- Set s to
- If x = 0, then
- Let m be the String value consisting of f + 1 occurrences of the code unit 0x0030 (DIGIT ZERO).
- Let e be 0.
- Else,
- If fractionDigits is not
undefined , then- Let e and n be
integers such that 10f ≤ n < 10f + 1 and for which n × 10e - f - x is as close to zero as possible. If there are two such sets of e and n, pick the e and n for which n × 10e - f is larger.
- Let e and n be
- Else,
- Let e, n, and ff be
integers such that ff ≥ 0, 10ff ≤ n < 10ff + 1,𝔽 (n × 10e - ff) is𝔽 (x), and ff is as small as possible. Note that the decimal representation of n has ff + 1 digits, n is not divisible by 10, and the least significant digit of n is not necessarily uniquely determined by these criteria. - Set f to ff.
- Let e, n, and ff be
- Let m be the String value consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
- If fractionDigits is not
- If f ≠ 0, then
- Let a be the first code unit of m.
- Let b be the other f code units of m.
- Set m to the
string-concatenation of a,"." , and b.
- If e = 0, then
- Let c be
"+" . - Let d be
"0" .
- Let c be
- Else,
- If e > 0, then
- Let c be
"+" .
- Let c be
- Else,
Assert : e < 0.- Let c be
"-" . - Set e to -e.
- Let d be the String value consisting of the digits of the decimal representation of e (in order, with no leading zeroes).
- If e > 0, then
- Set m to the
string-concatenation of m,"e" , c, and d. - Return the
string-concatenation of s and m.
For implementations that provide more accurate conversions than required by the rules above, it
is
recommended that the following alternative version of step
- Let e, n, and f be
integers such that f ≥ 0, 10f ≤ n < 10f + 1,𝔽 (n × 10e - f) is𝔽 (x), and f is as small as possible. If there are multiple possibilities for n, choose the value of n for which𝔽 (n × 10e - f) is closest in value to𝔽 (x). If there are two such possible values of n, choose the one that is even.
21.1.3.3 Number.prototype.toFixed ( fractionDigits )
This method returns a String containing this Number value represented in decimal fixed-point
notation
with fractionDigits digits after the decimal point. If fractionDigits is
It performs the following steps when called:
- Let x be ?
ThisNumberValue (this value). - Let f be ?
ToIntegerOrInfinity (fractionDigits). Assert : If fractionDigits isundefined , then f is 0.- If f is not
finite , throw aRangeError exception. - If f < 0 or f > 100, throw a
RangeError exception. - If x is not
finite , returnNumber::toString (x, 10). - Set x to
ℝ (x). - Let s be the empty String.
- If x < 0, then
- Set s to
"-" . - Set x to -x.
- Set s to
- If x ≥ 1021, then
- Else,
- Let n be an
integer for which n / 10f - x is as close to zero as possible. If there are two such n, pick the larger n. - If n = 0, let m be
"0" . Otherwise, let m be the String value consisting of the digits of the decimal representation of n (in order, with no leading zeroes). - If f ≠ 0, then
- Let k be the length of m.
- If k ≤ f, then
- Let z be the String value consisting of f + 1 - k occurrences of the code unit 0x0030 (DIGIT ZERO).
- Set m to the
string-concatenation of z and m. - Set k to f + 1.
- Let a be the first k - f code units of m.
- Let b be the other f code units of m.
- Set m to the
string-concatenation of a,"." , and b.
- Let n be an
- Return the
string-concatenation of s and m.
The output of toFixed may be more precise than toString for some values
because toString only prints enough significant digits to distinguish the number from adjacent
Number
values. For example,
(1000000000000000128).toString() returns
(1000000000000000128).toFixed(0) returns
21.1.3.4 Number.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method produces a String value that represents this Number value formatted according to the
conventions of the toString.
The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.1.3.5 Number.prototype.toPrecision ( precision )
This method returns a String containing this Number value represented either in decimal exponential
notation with one digit before the significand's decimal point and
It performs the following steps when called:
- Let x be ?
ThisNumberValue (this value). - If precision is
undefined , return !ToString (x). - Let p be ?
ToIntegerOrInfinity (precision). - If x is not
finite , returnNumber::toString (x, 10). - If p < 1 or p > 100, throw a
RangeError exception. - Set x to
ℝ (x). - Let s be the empty String.
- If x < 0, then
- Set s to the code unit 0x002D (HYPHEN-MINUS).
- Set x to -x.
- If x = 0, then
- Let m be the String value consisting of p occurrences of the code unit 0x0030 (DIGIT ZERO).
- Let e be 0.
- Else,
- Let e and n be
integers such that 10p - 1 ≤ n < 10p and for which n × 10e - p + 1 - x is as close to zero as possible. If there are two such sets of e and n, pick the e and n for which n × 10e - p + 1 is larger. - Let m be the String value consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
- If e < -6 or e ≥ p,
then
Assert : e ≠ 0.- If p ≠ 1, then
- Let a be the first code unit of m.
- Let b be the other p - 1 code units of m.
- Set m to the
string-concatenation of a,"." , and b.
- If e > 0, then
- Let c be the code unit 0x002B (PLUS SIGN).
- Else,
Assert : e < 0.- Let c be the code unit 0x002D (HYPHEN-MINUS).
- Set e to -e.
- Let d be the String value consisting of the digits of the decimal representation of e (in order, with no leading zeroes).
- Return the
string-concatenation of s, m, the code unit 0x0065 (LATIN SMALL LETTER E), c, and d.
- Let e and n be
- If e = p - 1, return the
string-concatenation of s and m. - If e ≥ 0, then
- Set m to the
string-concatenation of the first e + 1 code units of m, the code unit 0x002E (FULL STOP), and the remaining p - (e + 1) code units of m.
- Set m to the
- Else,
- Set m to the
string-concatenation of the code unit 0x0030 (DIGIT ZERO), the code unit 0x002E (FULL STOP), -(e + 1) occurrences of the code unit 0x0030 (DIGIT ZERO), and the String m.
- Set m to the
- Return the
string-concatenation of s and m.
21.1.3.6 Number.prototype.toString ( [ radix ] )
The optional radix should be an
This method performs the following steps when called:
- Let x be ?
ThisNumberValue (this value). - If radix is
undefined , let radixMV be 10. - Else, let radixMV be ?
ToIntegerOrInfinity (radix). - If radixMV is not in the
inclusive interval from 2 to 36, throw aRangeError exception. - Return
Number::toString (x, radixMV).
This method is not generic; it throws a
The
21.1.3.7 Number.prototype.valueOf ( )
- Return ?
ThisNumberValue (this value).
21.1.3.7.1 ThisNumberValue ( value )
The abstract operation ThisNumberValue takes argument value (an
- If value
is a Number , return value. - If value
is an Object and value has a [[NumberData]] internal slot, then- Let n be value.[[NumberData]].
Assert : nis a Number .- Return n.
- Throw a
TypeError exception.
21.1.4 Properties of Number Instances
Number instances are
21.2 BigInt Objects
21.2.1 The BigInt Constructor
The BigInt
- is %BigInt%.
- is the initial value of the
"BigInt" property of theglobal object . - performs a type conversion when called as a function rather than as a
constructor . - is not intended to be used with the
newoperator or to be subclassed. It may be used as the value of anextendsclause of a class definition but asupercall to the BigIntconstructor will cause an exception.
21.2.1.1 BigInt ( value )
This function performs the following steps when called:
- If NewTarget is not
undefined , throw aTypeError exception. - Let prim be ?
ToPrimitive (value,number ). - If prim
is a Number , return ?NumberToBigInt (prim). - Otherwise, return ?
ToBigInt (prim).
21.2.1.1.1 NumberToBigInt ( number )
The abstract operation NumberToBigInt takes argument number (a Number) and returns
either
a
- If
IsIntegralNumber (number) isfalse , throw aRangeError exception. - Return
ℤ (ℝ (number)).
21.2.2 Properties of the BigInt Constructor
The BigInt
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
21.2.2.1 BigInt.asIntN ( bits, bigint )
This function performs the following steps when called:
21.2.2.2 BigInt.asUintN ( bits, bigint )
This function performs the following steps when called:
21.2.2.3 BigInt.prototype
The initial value of BigInt.prototype is the
This property has the attributes { [[Writable]]:
21.2.3 Properties of the BigInt Prototype Object
The BigInt prototype object:
- is %BigInt.prototype%.
- is an
ordinary object . is not a BigInt object; it does not have a [[BigIntData]] internal slot.- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
The phrase “this BigInt value” within the specification of a method refers to the result returned by
calling the abstract operation
21.2.3.1 BigInt.prototype.constructor
The initial value of BigInt.prototype.constructor is
21.2.3.2 BigInt.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method produces a String value that represents this BigInt value formatted according to the
conventions of the toString.
The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.2.3.3 BigInt.prototype.toString ( [ radix ] )
The optional radix should be an
This method performs the following steps when called:
- Let x be ?
ThisBigIntValue (this value). - If radix is
undefined , let radixMV be 10. - Else, let radixMV be ?
ToIntegerOrInfinity (radix). - If radixMV is not in the
inclusive interval from 2 to 36, throw aRangeError exception. - Return
BigInt::toString (x, radixMV).
This method is not generic; it throws a
21.2.3.4 BigInt.prototype.valueOf ( )
- Return ?
ThisBigIntValue (this value).
21.2.3.4.1 ThisBigIntValue ( value )
The abstract operation ThisBigIntValue takes argument value (an
- If value
is a BigInt , return value. - If value
is an Object and value has a [[BigIntData]] internal slot, thenAssert : value.[[BigIntData]]is a BigInt .- Return value.[[BigIntData]].
- Throw a
TypeError exception.
21.2.3.5 BigInt.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
21.2.4 Properties of BigInt Instances
BigInt instances are
21.3 The Math Object
The Math object:
- is %Math%.
- is the initial value of the
"Math" property of theglobal object . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is not a
function object . - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a [[Call]] internal method; it cannot be invoked as a function.
In this specification, the phrase “the
21.3.1 Value Properties of the Math Object
21.3.1.1 Math.E
The
This property has the attributes { [[Writable]]:
21.3.1.2 Math.LN10
The
This property has the attributes { [[Writable]]:
21.3.1.3 Math.LN2
The
This property has the attributes { [[Writable]]:
21.3.1.4 Math.LOG10E
The
This property has the attributes { [[Writable]]:
The value of Math.LOG10E is approximately the reciprocal of the value of
Math.LN10.
21.3.1.5 Math.LOG2E
The
This property has the attributes { [[Writable]]:
The value of Math.LOG2E is approximately the reciprocal of the value of
Math.LN2.
21.3.1.6 Math.PI
The
This property has the attributes { [[Writable]]:
21.3.1.7 Math.SQRT1_2
The
This property has the attributes { [[Writable]]:
The value of Math.SQRT1_2 is approximately the reciprocal of the value of
Math.SQRT2.
21.3.1.8 Math.SQRT2
The
This property has the attributes { [[Writable]]:
21.3.1.9 Math [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
21.3.2 Function Properties of the Math Object
The behaviour of the functions acos, acosh, asin,
asinh, atan, atanh, atan2, cbrt,
cos, cosh, exp, expm1, hypot,
log, log1p, log2, log10, pow,
random, sin, sinh, sqrt, tan, and
tanh is not precisely specified here except to require specific results for certain
argument values that represent boundary cases of interest. For other argument values, these
functions
are intended to compute approximations to the results of familiar mathematical functions, but some
latitude is allowed in the choice of approximation algorithms. The general intent is that an
implementer
should be able to use the same mathematical library for ECMAScript on a given hardware platform that
is
available to C programmers on that platform.
Although the choice of algorithms is left to the implementation, it is recommended (but not
specified
by this standard) that implementations use the approximation algorithms for fdlibm, the freely distributable
mathematical library from Sun Microsystems (http://www.netlib.org/fdlibm).
21.3.2.1 Math.abs ( x )
This function returns the absolute value of x; the result has the same magnitude as x but has positive sign.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , returnNaN . - If n is
-0 𝔽, return+0 𝔽. - If n is
-∞ 𝔽, return+∞ 𝔽. - If n <
-0 𝔽, return -n. - Return n.
21.3.2.2 Math.acos ( x )
This function returns the inverse cosine of x. The result is expressed in radians and is
in
the
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , n >1 𝔽, or n <-1 𝔽, returnNaN . - If n is
1 𝔽, return+0 𝔽. - Return an
implementation-approximated Number value representing the result of the inverse cosine ofℝ (n).
21.3.2.3 Math.acosh ( x )
This function returns the inverse hyperbolic cosine of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is
1 𝔽, return+0 𝔽. - If n <
1 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the inverse hyperbolic cosine ofℝ (n).
21.3.2.4 Math.asin ( x )
This function returns the inverse sine of x. The result is expressed in radians and is in
the
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n >
1 𝔽 or n <-1 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the inverse sine ofℝ (n).
21.3.2.5 Math.asinh ( x )
This function returns the inverse hyperbolic sine of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - Return an
implementation-approximated Number value representing the result of the inverse hyperbolic sine ofℝ (n).
21.3.2.6 Math.atan ( x )
This function returns the inverse tangent of x. The result is expressed in radians and is
in
the
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n is
+∞ 𝔽, return animplementation-approximated Number value representing π / 2. - If n is
-∞ 𝔽, return animplementation-approximated Number value representing -π / 2. - Return an
implementation-approximated Number value representing the result of the inverse tangent ofℝ (n).
21.3.2.7 Math.atanh ( x )
This function returns the inverse hyperbolic tangent of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n >
1 𝔽 or n <-1 𝔽, returnNaN . - If n is
1 𝔽, return+∞ 𝔽. - If n is
-1 𝔽, return-∞ 𝔽. - Return an
implementation-approximated Number value representing the result of the inverse hyperbolic tangent ofℝ (n).
21.3.2.8 Math.atan2 ( y, x )
This function returns the inverse tangent of the quotient
It performs the following steps when called:
- Let ny be ?
ToNumber (y). - Let nx be ?
ToNumber (x). - If ny is
NaN or nx isNaN , returnNaN . - If ny is
+∞ 𝔽, then- If nx is
+∞ 𝔽, return animplementation-approximated Number value representing π / 4. - If nx is
-∞ 𝔽, return animplementation-approximated Number value representing 3π / 4. - Return an
implementation-approximated Number value representing π / 2.
- If nx is
- If ny is
-∞ 𝔽, then- If nx is
+∞ 𝔽, return animplementation-approximated Number value representing -π / 4. - If nx is
-∞ 𝔽, return animplementation-approximated Number value representing -3π / 4. - Return an
implementation-approximated Number value representing -π / 2.
- If nx is
- If ny is
+0 𝔽, then- If nx >
+0 𝔽 or nx is+0 𝔽, return+0 𝔽. - Return an
implementation-approximated Number value representing π.
- If nx >
- If ny is
-0 𝔽, then- If nx >
+0 𝔽 or nx is+0 𝔽, return-0 𝔽. - Return an
implementation-approximated Number value representing -π.
- If nx >
Assert : ny isfinite and is neither+0 𝔽 nor-0 𝔽.- If ny >
+0 𝔽, then- If nx is
+∞ 𝔽, return+0 𝔽. - If nx is
-∞ 𝔽, return animplementation-approximated Number value representing π. - If nx is either
+0 𝔽 or-0 𝔽, return animplementation-approximated Number value representing π / 2.
- If nx is
- If ny <
-0 𝔽, then- If nx is
+∞ 𝔽, return-0 𝔽. - If nx is
-∞ 𝔽, return animplementation-approximated Number value representing -π. - If nx is either
+0 𝔽 or-0 𝔽, return animplementation-approximated Number value representing -π / 2.
- If nx is
Assert : nx isfinite and is neither+0 𝔽 nor-0 𝔽.- Let r be the inverse tangent of
abs (ℝ (ny) /ℝ (nx)). - If nx <
-0 𝔽, then- If ny >
+0 𝔽, set r to π - r. - Else, set r to -π + r.
- If ny >
- Else,
- If ny <
-0 𝔽, set r to -r.
- If ny <
- Return an
implementation-approximated Number value representing r.
21.3.2.9 Math.cbrt ( x )
This function returns the cube root of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - Return an
implementation-approximated Number value representing the result of the cube root ofℝ (n).
21.3.2.10 Math.ceil ( x )
This function returns the smallest (closest to -∞)
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - If n <
-0 𝔽 and n >-1 𝔽, return-0 𝔽. - If n is an
integral Number , return n. - Return the smallest (closest to -∞)
integral Number value that is not less than n.
The value of Math.ceil(x) is the same as the value of -Math.floor(-x).
21.3.2.11 Math.clz32 ( x )
This function performs the following steps when called:
If n is either
21.3.2.12 Math.cos ( x )
This function returns the cosine of x. The argument is expressed in radians.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite , returnNaN . - If n is either
+0 𝔽 or-0 𝔽, return1 𝔽. - Return an
implementation-approximated Number value representing the result of the cosine ofℝ (n).
21.3.2.13 Math.cosh ( x )
This function returns the hyperbolic cosine of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , returnNaN . - If n is either
+∞ 𝔽 or-∞ 𝔽, return+∞ 𝔽. - If n is either
+0 𝔽 or-0 𝔽, return1 𝔽. - Return an
implementation-approximated Number value representing the result of the hyperbolic cosine ofℝ (n).
The value of Math.cosh(x) is the same as the value of
(Math.exp(x) + Math.exp(-x)) / 2.
21.3.2.14 Math.exp ( x )
This function returns the exponential function of x (e raised to the power of x, where e is the base of the natural logarithms).
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is either
+0 𝔽 or-0 𝔽, return1 𝔽. - If n is
-∞ 𝔽, return+0 𝔽. - Return an
implementation-approximated Number value representing the result of the exponential function ofℝ (n).
21.3.2.15 Math.expm1 ( x )
This function returns the result of subtracting 1 from the exponential function of x (e raised to the power of x, where e is the base of the natural logarithms). The result is computed in a way that is accurate even when the value of x is close to 0.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽,-0 𝔽, or+∞ 𝔽, return n. - If n is
-∞ 𝔽, return-1 𝔽. - Return an
implementation-approximated Number value representing the result of subtracting 1 from the exponential function ofℝ (n).
21.3.2.16 Math.floor ( x )
This function returns the greatest (closest to +∞)
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - If n <
1 𝔽 and n >+0 𝔽, return+0 𝔽. - If n is an
integral Number , return n. - Return the greatest (closest to +∞)
integral Number value that is not greater than n.
The value of Math.floor(x) is the same as the value of -Math.ceil(-x).
21.3.2.17 Math.fround ( x )
This function performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , returnNaN . - If n is one of
+0 𝔽,-0 𝔽,+∞ 𝔽, or-∞ 𝔽, return n. - Let n32 be the result of converting n
to
IEEE 754-2019 binary32 format using roundTiesToEven mode. - Let n64 be the result of converting n32
to
IEEE 754-2019 binary64 format. - Return the ECMAScript Number value corresponding to n64.
21.3.2.18 Math.hypot ( ...args )
Given zero or more arguments, this function returns the square root of the sum of squares of its arguments.
It performs the following steps when called:
- Let coerced be a new empty
List . - For each element arg of args, do
- Let n be ?
ToNumber (arg). - Append n to coerced.
- Let n be ?
- For each element number of coerced, do
- If number is either
+∞ 𝔽 or-∞ 𝔽, return+∞ 𝔽.
- If number is either
- Let onlyZero be
true . - For each element number of coerced, do
- If number is
NaN , returnNaN . - If number is neither
+0 𝔽 nor-0 𝔽, set onlyZero tofalse .
- If number is
- If onlyZero is
true , return+0 𝔽. - Return an
implementation-approximated Number value representing the square root of the sum of squares of themathematical values of the elements of coerced.
The
Implementations should take care to avoid the loss of precision from overflows and underflows that are prone to occur in naive implementations when this function is called with two or more arguments.
21.3.2.19 Math.imul ( x, y )
This function performs the following steps when called:
21.3.2.20 Math.log ( x )
This function returns the natural logarithm of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is
1 𝔽, return+0 𝔽. - If n is either
+0 𝔽 or-0 𝔽, return-∞ 𝔽. - If n <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the natural logarithm ofℝ (n).
21.3.2.21 Math.log1p ( x )
This function returns the natural logarithm of 1 + x. The result is computed in a way that is accurate even when the value of x is close to zero.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽,-0 𝔽, or+∞ 𝔽, return n. - If n is
-1 𝔽, return-∞ 𝔽. - If n <
-1 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the natural logarithm of 1 +ℝ (n).
21.3.2.22 Math.log10 ( x )
This function returns the base 10 logarithm of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is
1 𝔽, return+0 𝔽. - If n is either
+0 𝔽 or-0 𝔽, return-∞ 𝔽. - If n <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the base 10 logarithm ofℝ (n).
21.3.2.23 Math.log2 ( x )
This function returns the base 2 logarithm of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is
1 𝔽, return+0 𝔽. - If n is either
+0 𝔽 or-0 𝔽, return-∞ 𝔽. - If n <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the base 2 logarithm ofℝ (n).
21.3.2.24 Math.max ( ...args )
Given zero or more arguments, this function calls
It performs the following steps when called:
- Let coerced be a new empty
List . - For each element arg of args, do
- Let n be ?
ToNumber (arg). - Append n to coerced.
- Let n be ?
- Let highest be
-∞ 𝔽. - For each element number of coerced, do
- If number is
NaN , returnNaN . - If number is
+0 𝔽 and highest is-0 𝔽, set highest to+0 𝔽. - If number > highest, set highest to number.
- If number is
- Return highest.
The comparison of values to determine the largest value is done using the
The
21.3.2.25 Math.min ( ...args )
Given zero or more arguments, this function calls
It performs the following steps when called:
- Let coerced be a new empty
List . - For each element arg of args, do
- Let n be ?
ToNumber (arg). - Append n to coerced.
- Let n be ?
- Let lowest be
+∞ 𝔽. - For each element number of coerced, do
- If number is
NaN , returnNaN . - If number is
-0 𝔽 and lowest is+0 𝔽, set lowest to-0 𝔽. - If number < lowest, set lowest to number.
- If number is
- Return lowest.
The comparison of values to determine the largest value is done using the
The
21.3.2.26 Math.pow ( base, exponent )
This function performs the following steps when called:
- Set base to ?
ToNumber (base). - Set exponent to ?
ToNumber (exponent). - Return
Number::exponentiate (base, exponent).
21.3.2.27 Math.random ( )
This function returns a Number value with positive sign, greater than or equal to
Each Math.random function created for distinct
21.3.2.28 Math.round ( x )
This function returns the Number value that is closest to x and is integral. If two
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is anintegral Number , return n. - If n <
0.5 𝔽 and n >+0 𝔽, return+0 𝔽. - If n <
-0 𝔽 and n ≥-0.5 𝔽, return-0 𝔽. - Return the
integral Number closest to n, preferring the Number closer to +∞ in the case of a tie.
Math.round(3.5) returns 4, but Math.round(-3.5) returns -3.
The value of Math.round(x) is not always the same as the value of
Math.floor(x + 0.5). When x is x is less than Math.round(x) returns
Math.floor(x + 0.5) returns
Math.round(x) may also differ from the value of
Math.floor(x + 0.5)because of internal rounding when computing x + 0.5.
21.3.2.29 Math.sign ( x )
This function returns the sign of x, indicating whether x is positive, negative, or zero.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n <
-0 𝔽, return-1 𝔽. - Return
1 𝔽.
21.3.2.30 Math.sin ( x )
This function returns the sine of x. The argument is expressed in radians.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n is either
+∞ 𝔽 or-∞ 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the sine ofℝ (n).
21.3.2.31 Math.sinh ( x )
This function returns the hyperbolic sine of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - Return an
implementation-approximated Number value representing the result of the hyperbolic sine ofℝ (n).
The value of Math.sinh(x) is the same as the value of
(Math.exp(x) - Math.exp(-x)) / 2.
21.3.2.32 Math.sqrt ( x )
This function returns the square root of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽,-0 𝔽, or+∞ 𝔽, return n. - If n <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the square root ofℝ (n).
21.3.2.33 Math.tan ( x )
This function returns the tangent of x. The argument is expressed in radians.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n is either
+∞ 𝔽 or-∞ 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the tangent ofℝ (n).
21.3.2.34 Math.tanh ( x )
This function returns the hyperbolic tangent of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n is
+∞ 𝔽, return1 𝔽. - If n is
-∞ 𝔽, return-1 𝔽. - Return an
implementation-approximated Number value representing the result of the hyperbolic tangent ofℝ (n).
The value of Math.tanh(x) is the same as the value of
(Math.exp(x) - Math.exp(-x)) / (Math.exp(x) + Math.exp(-x)).
21.3.2.35 Math.trunc ( x )
This function returns the integral part of the number x, removing any fractional digits. If x is already integral, the result is x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - If n <
1 𝔽 and n >+0 𝔽, return+0 𝔽. - If n <
-0 𝔽 and n >-1 𝔽, return-0 𝔽. - Return the
integral Number nearest n in the direction of+0 𝔽.
21.4 Date Objects
21.4.1 Overview of Date Objects and Definitions of Abstract Operations
The following
21.4.1.1 Time Values and Time Range
Time measurement in ECMAScript is analogous to time measurement in POSIX, in particular sharing definition in terms of the proleptic Gregorian calendar, an epoch of midnight at the beginning of 1 January 1970 UTC, and an accounting of every day as comprising exactly 86,400 seconds (each of which is 1000 milliseconds long).
An ECMAScript time value
Time values do not account for UTC leap seconds—there are no time values representing instants within positive leap seconds, and there are time values representing instants removed from the UTC timeline by negative leap seconds. However, the definition of time values nonetheless yields piecewise alignment with UTC, with discontinuities only at leap second boundaries and zero difference outside of leap seconds.
A Number can exactly represent all
The exact moment of midnight at the beginning of 1 January 1970 UTC is represented by the time value
In the proleptic Gregorian calendar, leap years are precisely those which are both divisible by 4 and either divisible by 400 or not divisible by 100.
The 400 year cycle of the proleptic Gregorian calendar contains 97 leap years. This yields an average of 365.2425 days per year, which is 31,556,952,000 milliseconds. Therefore, the maximum range a Number could represent exactly with millisecond precision is approximately -285,426 to 285,426 years relative to 1970. The smaller range supported by a time value as specified in this section is approximately -273,790 to 273,790 years relative to 1970.
21.4.1.2 Time-related Constants
These constants are referenced by algorithms in the following sections.
21.4.1.3 Day ( t )
The abstract operation Day takes argument t (a
21.4.1.4 TimeWithinDay ( t )
The abstract operation TimeWithinDay takes argument t (a
21.4.1.5 DaysInYear ( y )
The abstract operation DaysInYear takes argument y (an
21.4.1.6 DayFromYear ( y )
The abstract operation DayFromYear takes argument y (an
- Let ry be
ℝ (y). - NOTE:
In
the following steps, numYears1, numYears4, numYears100, and
numYears400 represent the number of years divisible by 1, 4, 100, and 400,
respectively,
that occur between the
epoch and the start of year y. The number is negative if y is before theepoch . - Let numYears1 be (ry - 1970).
- Let numYears4 be
floor ((ry - 1969) / 4). - Let numYears100 be
floor ((ry - 1901) / 100). - Let numYears400 be
floor ((ry - 1601) / 400). - Return
𝔽 (365 × numYears1 + numYears4 - numYears100 + numYears400).
21.4.1.7 TimeFromYear ( y )
The abstract operation TimeFromYear takes argument y (an
- Return
msPerDay ×DayFromYear (y).
21.4.1.8 YearFromTime ( t )
The abstract operation YearFromTime takes argument t (a
- Return the largest
integral Number y (closest to +∞) such thatTimeFromYear (y) ≤ t.
21.4.1.9 DayWithinYear ( t )
The abstract operation DayWithinYear takes argument t (a
- Return
Day (t) -DayFromYear (YearFromTime (t)).
21.4.1.10 InLeapYear ( t )
The abstract operation InLeapYear takes argument t (a
- If
DaysInYear (YearFromTime (t)) is366 𝔽, return1 𝔽; else return+0 𝔽.
21.4.1.11 MonthFromTime ( t )
The abstract operation MonthFromTime takes argument t (a
- Let inLeapYear be
InLeapYear (t). - Let dayWithinYear be
DayWithinYear (t). - If dayWithinYear <
31 𝔽, return+0 𝔽. - If dayWithinYear <
59 𝔽 + inLeapYear, return1 𝔽. - If dayWithinYear <
90 𝔽 + inLeapYear, return2 𝔽. - If dayWithinYear <
120 𝔽 + inLeapYear, return3 𝔽. - If dayWithinYear <
151 𝔽 + inLeapYear, return4 𝔽. - If dayWithinYear <
181 𝔽 + inLeapYear, return5 𝔽. - If dayWithinYear <
212 𝔽 + inLeapYear, return6 𝔽. - If dayWithinYear <
243 𝔽 + inLeapYear, return7 𝔽. - If dayWithinYear <
273 𝔽 + inLeapYear, return8 𝔽. - If dayWithinYear <
304 𝔽 + inLeapYear, return9 𝔽. - If dayWithinYear <
334 𝔽 + inLeapYear, return10 𝔽. Assert : dayWithinYear <365 𝔽 + inLeapYear.- Return
11 𝔽.
21.4.1.12 DateFromTime ( t )
The abstract operation DateFromTime takes argument t (a
- Let inLeapYear be
InLeapYear (t). - Let dayWithinYear be
DayWithinYear (t). - Let month be
MonthFromTime (t). - If month is
+0 𝔽, return dayWithinYear +1 𝔽. - If month is
1 𝔽, return dayWithinYear -30 𝔽. - If month is
2 𝔽, return dayWithinYear -58 𝔽 - inLeapYear. - If month is
3 𝔽, return dayWithinYear -89 𝔽 - inLeapYear. - If month is
4 𝔽, return dayWithinYear -119 𝔽 - inLeapYear. - If month is
5 𝔽, return dayWithinYear -150 𝔽 - inLeapYear. - If month is
6 𝔽, return dayWithinYear -180 𝔽 - inLeapYear. - If month is
7 𝔽, return dayWithinYear -211 𝔽 - inLeapYear. - If month is
8 𝔽, return dayWithinYear -242 𝔽 - inLeapYear. - If month is
9 𝔽, return dayWithinYear -272 𝔽 - inLeapYear. - If month is
10 𝔽, return dayWithinYear -303 𝔽 - inLeapYear. Assert : month is11 𝔽.- Return dayWithinYear -
333 𝔽 - inLeapYear.
21.4.1.13 WeekDay ( t )
The abstract operation WeekDay takes argument t (a
21.4.1.14 HourFromTime ( t )
The abstract operation HourFromTime takes argument t (a
21.4.1.15 MinFromTime ( t )
The abstract operation MinFromTime takes argument t (a
- Return
𝔽 (floor (ℝ (t /msPerMinute ))modulo MinutesPerHour ).
21.4.1.16 SecFromTime ( t )
The abstract operation SecFromTime takes argument t (a
- Return
𝔽 (floor (ℝ (t /msPerSecond ))modulo SecondsPerMinute ).
21.4.1.17 msFromTime ( t )
The abstract operation msFromTime takes argument t (a
- Return
𝔽 (ℝ (t)modulo ℝ (msPerSecond )).
21.4.1.18 GetUTCEpochNanoseconds ( year, month, day, hour, minute, second, millisecond, microsecond, nanosecond )
The abstract operation GetUTCEpochNanoseconds takes arguments year (an
21.4.1.19 Time Zone Identifiers
Time zones in ECMAScript are represented by time
zone
identifiers, which are Strings composed entirely of code units in the
A primary time zone identifier is the preferred identifier for an available named time zone. A non-primary time zone identifier is an identifier for an available named time zone that is not a primary time zone identifier. An available named time zone identifier is either a primary time zone identifier or a non-primary time zone identifier. Each available named time zone identifier is associated with exactly one available named time zone. Each available named time zone is associated with exactly one primary time zone identifier and zero or more non-primary time zone identifiers.
ECMAScript implementations must support an available named time zone with the identifier
Implementations that follow the requirements for time zones as described in the ECMA-402
Internationalization API specification are called time zone aware.
Time zone aware implementations must support available named time zones corresponding to the Zone and
Link
names of the IANA Time Zone Database, and only such names.
In time zone aware implementations, a primary time zone identifier is a Zone name, and a non-primary
time
zone identifier is a Link name, respectively, in the IANA Time Zone Database except as specifically
overridden by
21.4.1.20 GetNamedTimeZoneEpochNanoseconds ( timeZoneIdentifier, year, month, day, hour, minute, second, millisecond, microsecond, nanosecond )
The
When the input represents a local time occurring more than once because of a negative time zone
transition
(e.g. when daylight saving time ends or the time zone offset is decreased due to a time zone rule
change),
the returned
The default implementation of GetNamedTimeZoneEpochNanoseconds, to be used for ECMAScript implementations that do not include local political rules for any time zones, performs the following steps when called:
Assert : timeZoneIdentifier is"UTC" .- Let epochNanoseconds be
GetUTCEpochNanoseconds (year, month, day, hour, minute, second, millisecond, microsecond, nanosecond). - Return « epochNanoseconds ».
It is required for
1:30 AM on 5 November 2017 in America/New_York is repeated twice, so
GetNamedTimeZoneEpochNanoseconds(
2:30 AM on 12 March 2017 in America/New_York does not exist, so
GetNamedTimeZoneEpochNanoseconds(
21.4.1.21 GetNamedTimeZoneOffsetNanoseconds ( timeZoneIdentifier, epochNanoseconds )
The
The returned
The default implementation of GetNamedTimeZoneOffsetNanoseconds, to be used for ECMAScript implementations that do not include local political rules for any time zones, performs the following steps when called:
Assert : timeZoneIdentifier is"UTC" .- Return 0.
Time zone offset values may be positive or negative.
21.4.1.22 Time Zone Identifier Record
A Time Zone Identifier Record is a
Time Zone Identifier Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Identifier]] | a String | An |
| [[PrimaryIdentifier]] | a String | The |
If [[Identifier]] is a
21.4.1.23 AvailableNamedTimeZoneIdentifiers ( )
The
- If the implementation does not include local political rules
for
any time zones, then
- Return « the
Time Zone Identifier Record { [[Identifier]]:"UTC" , [[PrimaryIdentifier]]:"UTC" } ».
- Return « the
- Let identifiers be the
List of uniqueavailable named time zone identifiers . - Sort identifiers into the
same
order as if an Array of the same values had been sorted using %Array.prototype.sort% with
undefined as comparefn. - Let result be a new empty
List . - For each element identifier of
identifiers,
do
- Let primary be identifier.
- If identifier is a
non-primary time zone identifier in this implementation and identifier is not"UTC" , then- Set primary to the
primary time zone identifier associated with identifier. - NOTE: An implementation may need to resolve
identifier iteratively to obtain the
primary time zone identifier .
- Set primary to the
- Let record be the
Time Zone Identifier Record { [[Identifier]]: identifier, [[PrimaryIdentifier]]: primary }. - Append record to result.
Assert : result contains aTime Zone Identifier Record r such that r.[[Identifier]] is"UTC" and r.[[PrimaryIdentifier]] is"UTC" .- Return result.
21.4.1.24 SystemTimeZoneIdentifier ( )
The
- If the implementation only supports the UTC time zone, return
"UTC" . - Let systemTimeZoneString be the String
representing
the
host environment 's current time zone, either aprimary time zone identifier or anoffset time zone identifier. - Return systemTimeZoneString.
To ensure the level of functionality that implementations commonly provide in the methods of the
Date
object, it is recommended that SystemTimeZoneIdentifier return an IANA time zone name
corresponding
to
the
For example, if the
21.4.1.25 LocalTime ( t )
The abstract operation LocalTime takes argument t (a
- Let systemTimeZoneIdentifier be
SystemTimeZoneIdentifier (). - If
IsTimeZoneOffsetString (systemTimeZoneIdentifier) istrue , then- Let offsetNs be
ParseTimeZoneOffsetString (systemTimeZoneIdentifier).
- Let offsetNs be
- Else,
- Let offsetNs be
GetNamedTimeZoneOffsetNanoseconds (systemTimeZoneIdentifier,ℤ (ℝ (t) × 106)).
- Let offsetNs be
- Let offsetMs be
truncate (offsetNs / 106). - Return t +
𝔽 (offsetMs).
If political rules for the local time t are not available within the implementation,
the
result is t because
It is required for
Two different input
21.4.1.26 UTC ( t )
The abstract operation UTC takes argument t (a Number) and returns a
- If t is not
finite , returnNaN . - Let systemTimeZoneIdentifier be
SystemTimeZoneIdentifier (). - If
IsTimeZoneOffsetString (systemTimeZoneIdentifier) istrue , then- Let offsetNs be
ParseTimeZoneOffsetString (systemTimeZoneIdentifier).
- Let offsetNs be
- Else,
- Let possibleInstants be
GetNamedTimeZoneEpochNanoseconds (systemTimeZoneIdentifier,ℝ (YearFromTime (t)),ℝ (MonthFromTime (t)) + 1,ℝ (DateFromTime (t)),ℝ (HourFromTime (t)),ℝ (MinFromTime (t)),ℝ (SecFromTime (t)),ℝ (msFromTime (t)), 0, 0). - NOTE: The following steps ensure that when t represents local time repeating multiple times at a negative time zone transition (e.g. when the daylight saving time ends or the time zone offset is decreased due to a time zone rule change) or skipped local time at a positive time zone transition (e.g. when the daylight saving time starts or the time zone offset is increased due to a time zone rule change), t is interpreted using the time zone offset before the transition.
- If possibleInstants is not empty, then
- Let disambiguatedInstant be possibleInstants[0].
- Else,
- NOTE: t represents a local time skipped at a positive time zone transition (e.g. due to daylight saving time starting or a time zone rule change increasing the UTC offset).
- Let
possibleInstantsBefore
be
GetNamedTimeZoneEpochNanoseconds (systemTimeZoneIdentifier,ℝ (YearFromTime (tBefore)),ℝ (MonthFromTime (tBefore)) + 1,ℝ (DateFromTime (tBefore)),ℝ (HourFromTime (tBefore)),ℝ (MinFromTime (tBefore)),ℝ (SecFromTime (tBefore)),ℝ (msFromTime (tBefore)), 0, 0), where tBefore is the largestintegral Number < t for which possibleInstantsBefore is not empty (i.e., tBefore represents the last local time before the transition). - Let disambiguatedInstant be the last element of possibleInstantsBefore.
- Let offsetNs be
GetNamedTimeZoneOffsetNanoseconds (systemTimeZoneIdentifier, disambiguatedInstant).
- Let possibleInstants be
- Let offsetMs be
truncate (offsetNs / 106). - Return t -
𝔽 (offsetMs).
Input t is nominally a
If political rules for the local time t are not available within the implementation, the
result is t because
It is required for
1:30 AM on 5 November 2017 in America/New_York is repeated twice (fall backward), but it must be
interpreted as 1:30 AM UTC-04 instead of 1:30 AM UTC-05.
In UTC(
2:30 AM on 12 March 2017 in America/New_York does not exist, but it must be interpreted as 2:30 AM
UTC-05 (equivalent to 3:30 AM UTC-04).
In UTC(
21.4.1.27 MakeTime ( hour, min, sec, ms )
The abstract operation MakeTime takes arguments hour (a Number), min (a Number), sec (a Number), and ms (a Number) and returns a Number. It calculates a number of milliseconds. It performs the following steps when called:
- If hour is not
finite , min is notfinite , sec is notfinite , or ms is notfinite , returnNaN . - Let h be
𝔽 (!ToIntegerOrInfinity (hour)). - Let m be
𝔽 (!ToIntegerOrInfinity (min)). - Let s be
𝔽 (!ToIntegerOrInfinity (sec)). - Let milli be
𝔽 (!ToIntegerOrInfinity (ms)). - Return ((h ×
msPerHour + m ×msPerMinute ) + s ×msPerSecond ) + milli.
The arithmetic in MakeTime is floating-point arithmetic, which is not associative, so the operations must be performed in the correct order.
21.4.1.28 MakeDay ( year, month, date )
The abstract operation MakeDay takes arguments year (a Number), month (a Number), and date (a Number) and returns a Number. It calculates a number of days. It performs the following steps when called:
- If year is not
finite , month is notfinite , or date is notfinite , returnNaN . - Let y be
𝔽 (!ToIntegerOrInfinity (year)). - Let m be
𝔽 (!ToIntegerOrInfinity (month)). - Let dt be
𝔽 (!ToIntegerOrInfinity (date)). - Let ym be y +
𝔽 (floor (ℝ (m) / 12)). - If ym is not
finite , returnNaN . - Let mn be
𝔽 (ℝ (m)modulo 12). - Find a
finite time value t such thatYearFromTime (t) is ym,MonthFromTime (t) is mn, andDateFromTime (t) is1 𝔽; but if this is not possible (because some argument is out of range), returnNaN . - Return
Day (t) + dt -1 𝔽.
21.4.1.29 MakeDate ( day, time )
The abstract operation MakeDate takes arguments day (a Number) and time (a Number) and returns a Number. It calculates a number of milliseconds. It performs the following steps when called:
21.4.1.30 MakeFullYear ( year )
The abstract operation MakeFullYear takes argument year (a Number) and returns an
- If year is
NaN , returnNaN . - Let truncated be !
ToIntegerOrInfinity (year). - If truncated is in the
inclusive interval from 0 to 99, return1900 𝔽 +𝔽 (truncated). - Return
𝔽 (truncated).
21.4.1.31 TimeClip ( time )
The abstract operation TimeClip takes argument time (a Number) and returns a Number. It calculates a number of milliseconds. It performs the following steps when called:
- If time is not
finite , returnNaN . - If
abs (ℝ (time)) > 8.64 × 1015, returnNaN . - Return
𝔽 (!ToIntegerOrInfinity (time)).
21.4.1.32 Date Time String Format
ECMAScript defines a string interchange format for date-times based upon a simplification of the ISO
8601
calendar date extended format. The format is as follows: YYYY-MM-DDTHH:mm:ss.sssZ
Where the elements are as follows:
YYYY
|
is the year in the proleptic Gregorian calendar as four decimal digits from 0000 to 9999, or
as
an
|
-
|
|
MM
|
is the month of the year as two decimal digits from 01 (January) to 12 (December). |
DD
|
is the day of the month as two decimal digits from 01 to 31. |
T
|
|
HH
|
is the number of complete hours that have passed since midnight as two decimal digits from 00 to 24. |
:
|
|
mm
|
is the number of complete minutes since the start of the hour as two decimal digits from 00 to 59. |
ss
|
is the number of complete seconds since the start of the minute as two decimal digits from 00 to 59. |
.
|
|
sss
|
is the number of complete milliseconds since the start of the second as three decimal digits. |
Z
|
is the UTC offset representation specified as HH:mm (a subset of the |
This format includes date-only forms:
YYYY
YYYY-MM
YYYY-MM-DD
It also includes “date-time” forms that consist of one of the above date-only forms immediately followed by one of the following time forms with an optional UTC offset representation appended:
THH:mm
THH:mm:ss
THH:mm:ss.sss
A string containing out-of-bounds or nonconforming elements is not a valid instance of this format.
As every day both starts and ends with midnight, the two notations 00:00 and
24:00 are available to distinguish the two midnights that can be associated with one
date. This means that the following two notations refer to exactly the same point in time:
1995-02-04T24:00 and 1995-02-05T00:00. This interpretation of the latter
form as "end of a calendar day" is consistent with ISO 8601, even though that specification
reserves
it for describing time intervals and does not permit it within representations of single points in
time.
There exists no international standard that specifies abbreviations for civil time zones like CET, EST, etc. and sometimes the same abbreviation is even used for two very different time zones. For this reason, both ISO 8601 and this format specify numeric representations of time zone offsets.
21.4.1.32.1 Expanded Years
Covering the full Date.parse
Examples of date-
| -271821-04-20T00:00:00Z | 271822 B.C. |
| -000001-01-01T00:00:00Z | 2 B.C. |
| +000000-01-01T00:00:00Z | 1 B.C. |
| +000001-01-01T00:00:00Z | 1 A.D. |
| +001970-01-01T00:00:00Z | 1970 A.D. |
| +002009-12-15T00:00:00Z | 2009 A.D. |
| +275760-09-13T00:00:00Z | 275760 A.D. |
21.4.1.33 Time Zone Offset String Format
ECMAScript defines a string interchange format for UTC offsets, derived from ISO 8601.
The format is described by the following grammar.
The usage of Unicode code points in this grammar is listed in
| Code Point | Unicode Name | Abbreviation |
|---|---|---|
U+2212
|
MINUS SIGN | <MINUS> |
Syntax
21.4.1.33.1 IsTimeZoneOffsetString ( offsetString )
The abstract operation IsTimeZoneOffsetString takes argument offsetString (a String) and
returns a Boolean. The return value indicates whether offsetString conforms to the
grammar
given by
- Let parseResult be
ParseText (StringToCodePoints (offsetString),UTCOffset ). - If parseResult is a
List of errors, returnfalse . - Return
true .
21.4.1.33.2 ParseTimeZoneOffsetString ( offsetString )
The abstract operation ParseTimeZoneOffsetString takes argument offsetString (a String)
and
returns an
- Let parseResult be
ParseText (StringToCodePoints (offsetString),UTCOffset ). Assert : parseResult is not aList of errors.Assert : parseResult contains aTemporalSign Parse Node .- Let parsedSign be the
source text matched by theTemporalSign Parse Node contained within parseResult. - If parsedSign is the single code point U+002D
(HYPHEN-MINUS) or U+2212 (MINUS SIGN), then
- Let sign be -1.
- Else,
- Let sign be 1.
- NOTE: Applications of
StringToNumber below do not lose precision, since each of the parsed values is guaranteed to be a sufficiently short string of decimal digits. Assert : parseResult contains anHour Parse Node .- Let parsedHours be the
source text matched by theHour Parse Node contained within parseResult. - Let hours be
ℝ (StringToNumber (CodePointsToString (parsedHours))). - If parseResult does not contain a
MinuteSecond Parse Node , then- Let minutes be 0.
- Else,
- Let parsedMinutes be the
source text matched by the firstMinuteSecond Parse Node contained within parseResult. - Let minutes be
ℝ (StringToNumber (CodePointsToString (parsedMinutes))).
- Let parsedMinutes be the
- If parseResult does not contain two
MinuteSecond Parse Nodes , then- Let seconds be 0.
- Else,
- Let parsedSeconds be the
source text matched by the secondMinuteSecond Parse Node contained within parseResult. - Let seconds be
ℝ (StringToNumber (CodePointsToString (parsedSeconds))).
- Let parsedSeconds be the
- If parseResult does not contain a
TemporalDecimalFraction Parse Node , then- Let nanoseconds be 0.
- Else,
- Let parsedFraction be the
source text matched by theTemporalDecimalFraction Parse Node contained within parseResult. - Let fraction be the
string-concatenation ofCodePointsToString (parsedFraction) and"000000000" . - Let nanosecondsString be the
substring of fraction from 1 to 10. - Let nanoseconds be
ℝ (StringToNumber (nanosecondsString)).
- Let parsedFraction be the
- Return sign × (((hours × 60 + minutes) × 60 + seconds) × 109 + nanoseconds).
21.4.2 The Date Constructor
The Date
- is %Date%.
- is the initial value of the
"Date" property of theglobal object . - creates and initializes a new Date when called as a
constructor . - returns a String representing the current time (UTC) when called as a function rather than as a
constructor . - is a function whose behaviour differs based upon the number and types of its arguments.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Date behaviour must include asupercall to the Dateconstructor to create and initialize the subclass instance with a [[DateValue]] internal slot.
21.4.2.1 Date ( ...values )
This function performs the following steps when called:
- If NewTarget is
undefined , then- Let now be the
time value (UTC) identifying the current time. - Return
ToDateString (now).
- Let now be the
- Let numberOfArgs be the number of elements in values.
- If numberOfArgs = 0, then
- Let dv be the
time value (UTC) identifying the current time.
- Let dv be the
- Else if numberOfArgs = 1, then
- Let value be values[0].
- If value
is an Object and value has a [[DateValue]] internal slot, then- Let tv be value.[[DateValue]].
- Else,
- Let v be ?
ToPrimitive (value). - If v
is a String , thenAssert : The next step never returns anabrupt completion because vis a String .- Let tv be the result of parsing
v as a date, in exactly the same manner as for the
parsemethod (21.4.3.2 ).
- Else,
- Let tv be ?
ToNumber (v).
- Let tv be ?
- Let v be ?
- Let dv be
TimeClip (tv).
- Else,
Assert : numberOfArgs ≥ 2.- Let y be ?
ToNumber (values[0]). - Let m be ?
ToNumber (values[1]). - If numberOfArgs > 2, let dt be
?
ToNumber (values[2]); else let dt be1 𝔽. - If numberOfArgs > 3, let h be
?
ToNumber (values[3]); else let h be+0 𝔽. - If numberOfArgs > 4, let min be
?
ToNumber (values[4]); else let min be+0 𝔽. - If numberOfArgs > 5, let s be
?
ToNumber (values[5]); else let s be+0 𝔽. - If numberOfArgs > 6, let milli
be
?
ToNumber (values[6]); else let milli be+0 𝔽. - Let yr be
MakeFullYear (y). - Let finalDate be
MakeDate (MakeDay (yr, m, dt),MakeTime (h, min, s, milli)). - Let dv be
TimeClip (UTC (finalDate)).
- Let O be ?
OrdinaryCreateFromConstructor (NewTarget,"%Date.prototype%" , « [[DateValue]] »). - Set O.[[DateValue]] to dv.
- Return O.
21.4.3 Properties of the Date Constructor
The Date
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is7 𝔽. - has the following properties:
21.4.3.1 Date.now ( )
This function returns the
21.4.3.2 Date.parse ( string )
This function applies the
If the String conforms to the MM or DD elements are absent, HH, mm, or ss elements are absent, sss element is absent,
If x is any Date whose milliseconds amount is zero within a particular implementation of
ECMAScript, then all of the following expressions should produce the same numeric value in that
implementation, if all the properties referenced have their initial values:
x.valueOf()
Date.parse(x.toString())
Date.parse(x.toUTCString())
Date.parse(x.toISOString())However, the expression
Date.parse(x.toLocaleString())is not required to produce the same Number value as the preceding three expressions and, in general,
the
value produced by this function is toString or toUTCString
method.
21.4.3.3 Date.prototype
The initial value of Date.prototype is the
This property has the attributes { [[Writable]]:
21.4.3.4 Date.UTC ( year [ , month [ , date [ , hours [ , minutes [ , seconds [ , ms ] ] ] ] ] ] )
This function performs the following steps when called:
- Let y be ?
ToNumber (year). - If month is present, let m be
?
ToNumber (month); else let m be+0 𝔽. - If date is present, let dt be
?
ToNumber (date); else let dt be1 𝔽. - If hours is present, let h be
?
ToNumber (hours); else let h be+0 𝔽. - If minutes is present, let min be
?
ToNumber (minutes); else let min be+0 𝔽. - If seconds is present, let s be
?
ToNumber (seconds); else let s be+0 𝔽. - If ms is present, let milli be
?
ToNumber (ms); else let milli be+0 𝔽. - Let yr be
MakeFullYear (y). - Return
TimeClip (MakeDate (MakeDay (yr, m, dt),MakeTime (h, min, s, milli))).
The
This function differs from the Date
21.4.4 Properties of the Date Prototype Object
The Date prototype object:
- is %Date.prototype%.
- is itself an
ordinary object . - is not a Date instance and does not have a [[DateValue]] internal slot.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
Unless explicitly defined otherwise, the methods of the Date prototype object defined below are not
generic
and the
21.4.4.1 Date.prototype.constructor
The initial value of Date.prototype.constructor is
21.4.4.2 Date.prototype.getDate ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
DateFromTime (LocalTime (t)).
21.4.4.3 Date.prototype.getDay ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
WeekDay (LocalTime (t)).
21.4.4.4 Date.prototype.getFullYear ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
YearFromTime (LocalTime (t)).
21.4.4.5 Date.prototype.getHours ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
HourFromTime (LocalTime (t)).
21.4.4.6 Date.prototype.getMilliseconds ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
msFromTime (LocalTime (t)).
21.4.4.7 Date.prototype.getMinutes ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
MinFromTime (LocalTime (t)).
21.4.4.8 Date.prototype.getMonth ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
MonthFromTime (LocalTime (t)).
21.4.4.9 Date.prototype.getSeconds ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
SecFromTime (LocalTime (t)).
21.4.4.10 Date.prototype.getTime ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Return dateObject.[[DateValue]].
21.4.4.11 Date.prototype.getTimezoneOffset ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return (t -
LocalTime (t)) /msPerMinute .
21.4.4.12 Date.prototype.getUTCDate ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
DateFromTime (t).
21.4.4.13 Date.prototype.getUTCDay ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
WeekDay (t).
21.4.4.14 Date.prototype.getUTCFullYear ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
YearFromTime (t).
21.4.4.15 Date.prototype.getUTCHours ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
HourFromTime (t).
21.4.4.16 Date.prototype.getUTCMilliseconds ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
msFromTime (t).
21.4.4.17 Date.prototype.getUTCMinutes ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
MinFromTime (t).
21.4.4.18 Date.prototype.getUTCMonth ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
MonthFromTime (t).
21.4.4.19 Date.prototype.getUTCSeconds ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
SecFromTime (t).
21.4.4.20 Date.prototype.setDate ( date )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let dt be ?
ToNumber (date). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - Let newDate be
MakeDate (MakeDay (YearFromTime (t),MonthFromTime (t), dt),TimeWithinDay (t)). - Let u be
TimeClip (UTC (newDate)). - Set dateObject.[[DateValue]] to u.
- Return u.
21.4.4.21 Date.prototype.setFullYear ( year [ , month [ , date ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let y be ?
ToNumber (year). - If t is
NaN , set t to+0 𝔽; otherwise, set t toLocalTime (t). - If month is not present, let m be
MonthFromTime (t); otherwise, let m be ?ToNumber (month). - If date is not present, let dt be
DateFromTime (t); otherwise, let dt be ?ToNumber (date). - Let newDate be
MakeDate (MakeDay (y, m, dt),TimeWithinDay (t)). - Let u be
TimeClip (UTC (newDate)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If month is not present, this method behaves as if month was present with
the
value getMonth(). If date is not present, it behaves as if date
was
present with the value getDate().
21.4.4.22 Date.prototype.setHours ( hour [ , min [ , sec [ , ms ] ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let h be ?
ToNumber (hour). - If min is present, let m be
?
ToNumber (min). - If sec is present, let s be
?
ToNumber (sec). - If ms is present, let milli be
?
ToNumber (ms). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - If min is not present, let m be
MinFromTime (t). - If sec is not present, let s be
SecFromTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (h, m, s, milli)). - Let u be
TimeClip (UTC (date)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If min is not present, this method behaves as if min was present with the
value
getMinutes(). If sec is not present, it behaves as if sec was
present with the value getSeconds(). If ms is not present, it behaves as
if
ms was present with the value getMilliseconds().
21.4.4.23 Date.prototype.setMilliseconds ( ms )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Set ms to ?
ToNumber (ms). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - Let time be
MakeTime (HourFromTime (t),MinFromTime (t),SecFromTime (t), ms). - Let u be
TimeClip (UTC (MakeDate (Day (t), time))). - Set dateObject.[[DateValue]] to u.
- Return u.
21.4.4.24 Date.prototype.setMinutes ( min [ , sec [ , ms ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let m be ?
ToNumber (min). - If sec is present, let s be
?
ToNumber (sec). - If ms is present, let milli be
?
ToNumber (ms). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - If sec is not present, let s be
SecFromTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (HourFromTime (t), m, s, milli)). - Let u be
TimeClip (UTC (date)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If sec is not present, this method behaves as if sec was present with the
value
getSeconds(). If ms is not present, this behaves as if ms was
present with the value getMilliseconds().
21.4.4.25 Date.prototype.setMonth ( month [ , date ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let m be ?
ToNumber (month). - If date is present, let dt be
?
ToNumber (date). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - If date is not present, let dt be
DateFromTime (t). - Let newDate be
MakeDate (MakeDay (YearFromTime (t), m, dt),TimeWithinDay (t)). - Let u be
TimeClip (UTC (newDate)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If date is not present, this method behaves as if date was present with the
value getDate().
21.4.4.26 Date.prototype.setSeconds ( sec [ , ms ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let s be ?
ToNumber (sec). - If ms is present, let milli be
?
ToNumber (ms). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (HourFromTime (t),MinFromTime (t), s, milli)). - Let u be
TimeClip (UTC (date)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If ms is not present, this method behaves as if ms was present with the
value
getMilliseconds().
21.4.4.27 Date.prototype.setTime ( time )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be ?
ToNumber (time). - Let v be
TimeClip (t). - Set dateObject.[[DateValue]] to v.
- Return v.
21.4.4.28 Date.prototype.setUTCDate ( date )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let dt be ?
ToNumber (date). - If t is
NaN , returnNaN . - Let newDate be
MakeDate (MakeDay (YearFromTime (t),MonthFromTime (t), dt),TimeWithinDay (t)). - Let v be
TimeClip (newDate). - Set dateObject.[[DateValue]] to v.
- Return v.
21.4.4.29 Date.prototype.setUTCFullYear ( year [ , month [ , date ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , set t to+0 𝔽. - Let y be ?
ToNumber (year). - If month is not present, let m be
MonthFromTime (t); otherwise, let m be ?ToNumber (month). - If date is not present, let dt be
DateFromTime (t); otherwise, let dt be ?ToNumber (date). - Let newDate be
MakeDate (MakeDay (y, m, dt),TimeWithinDay (t)). - Let v be
TimeClip (newDate). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If month is not present, this method behaves as if month was present with
the
value getUTCMonth(). If date is not present, it behaves as if
date
was present with the value getUTCDate().
21.4.4.30 Date.prototype.setUTCHours ( hour [ , min [ , sec [ , ms ] ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let h be ?
ToNumber (hour). - If min is present, let m be
?
ToNumber (min). - If sec is present, let s be
?
ToNumber (sec). - If ms is present, let milli be
?
ToNumber (ms). - If t is
NaN , returnNaN . - If min is not present, let m be
MinFromTime (t). - If sec is not present, let s be
SecFromTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (h, m, s, milli)). - Let v be
TimeClip (date). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If min is not present, this method behaves as if min was present with the
value
getUTCMinutes(). If sec is not present, it behaves as if sec
was
present with the value getUTCSeconds(). If ms is not present, it behaves
as
if
ms was present with the value getUTCMilliseconds().
21.4.4.31 Date.prototype.setUTCMilliseconds ( ms )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Set ms to ?
ToNumber (ms). - If t is
NaN , returnNaN . - Let time be
MakeTime (HourFromTime (t),MinFromTime (t),SecFromTime (t), ms). - Let v be
TimeClip (MakeDate (Day (t), time)). - Set dateObject.[[DateValue]] to v.
- Return v.
21.4.4.32 Date.prototype.setUTCMinutes ( min [ , sec [ , ms ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let m be ?
ToNumber (min). - If sec is present, let s be
?
ToNumber (sec). - If ms is present, let milli be
?
ToNumber (ms). - If t is
NaN , returnNaN . - If sec is not present, let s be
SecFromTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (HourFromTime (t), m, s, milli)). - Let v be
TimeClip (date). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If sec is not present, this method behaves as if sec was present with the
value
getUTCSeconds(). If ms is not present, it behaves as if ms was
present with the value return by getUTCMilliseconds().
21.4.4.33 Date.prototype.setUTCMonth ( month [ , date ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let m be ?
ToNumber (month). - If date is present, let dt be
?
ToNumber (date). - If t is
NaN , returnNaN . - If date is not present, let dt be
DateFromTime (t). - Let newDate be
MakeDate (MakeDay (YearFromTime (t), m, dt),TimeWithinDay (t)). - Let v be
TimeClip (newDate). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If date is not present, this method behaves as if date was present with the
value getUTCDate().
21.4.4.34 Date.prototype.setUTCSeconds ( sec [ , ms ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let s be ?
ToNumber (sec). - If ms is present, let milli be
?
ToNumber (ms). - If t is
NaN , returnNaN . - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (HourFromTime (t),MinFromTime (t), s, milli)). - Let v be
TimeClip (date). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If ms is not present, this method behaves as if ms was present with the
value
getUTCMilliseconds().
21.4.4.35 Date.prototype.toDateString ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- If tv is
NaN , return"Invalid Date" . - Let t be
LocalTime (tv). - Return
DateString (t).
21.4.4.36 Date.prototype.toISOString ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- If tv is not
finite , throw aRangeError exception. - If tv corresponds with a year that cannot be
represented in the
Date Time String Format , throw aRangeError exception. - Return a String representation of tv in the
Date Time String Format on the UTC time scale, including all format elements and the UTC offset representation"Z" .
21.4.4.37 Date.prototype.toJSON ( key )
This method provides a String representation of a Date for use by JSON.stringify
(
It performs the following steps when called:
- Let O be ?
ToObject (this value). - Let tv be ?
ToPrimitive (O,number ). - If tv
is a Number and tv is notfinite , returnnull . - Return ?
Invoke (O,"toISOString" ).
The argument is ignored.
This method is intentionally generic; it does not require that its toISOString method.
21.4.4.38 Date.prototype.toLocaleDateString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a String value. The contents of the String are
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.4.4.39 Date.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a String value. The contents of the String are
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.4.4.40 Date.prototype.toLocaleTimeString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a String value. The contents of the String are
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.4.4.41 Date.prototype.toString ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- Return
ToDateString (tv).
For any Date d such that d.[[DateValue]] is
evenly
divisible by 1000, the result of Date.parse(d.toString()) = d.valueOf().
See
This method is not generic; it throws a
21.4.4.41.1 TimeString ( tv )
The abstract operation TimeString takes argument tv (a Number, but not
- Let hour be
ToZeroPaddedDecimalString (ℝ (HourFromTime (tv)), 2). - Let minute be
ToZeroPaddedDecimalString (ℝ (MinFromTime (tv)), 2). - Let second be
ToZeroPaddedDecimalString (ℝ (SecFromTime (tv)), 2). - Return the
string-concatenation of hour,":" , minute,":" , second, the code unit 0x0020 (SPACE), and"GMT" .
21.4.4.41.2 DateString ( tv )
The abstract operation DateString takes argument tv (a Number, but not
- Let weekday be the Name of the entry in
Table 63 with the NumberWeekDay (tv). - Let month be the Name of the entry in
Table 64 with the NumberMonthFromTime (tv). - Let day be
ToZeroPaddedDecimalString (ℝ (DateFromTime (tv)), 2). - Let yv be
YearFromTime (tv). - If yv is
+0 𝔽 or yv >+0 𝔽, let yearSign be the empty String; otherwise, let yearSign be"-" . - Let paddedYear be
ToZeroPaddedDecimalString (abs (ℝ (yv)), 4). - Return the
string-concatenation of weekday, the code unit 0x0020 (SPACE), month, the code unit 0x0020 (SPACE), day, the code unit 0x0020 (SPACE), yearSign, and paddedYear.
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21.4.4.41.3 TimeZoneString ( tv )
The abstract operation TimeZoneString takes argument tv (an
- Let systemTimeZoneIdentifier be
SystemTimeZoneIdentifier (). - If
IsTimeZoneOffsetString (systemTimeZoneIdentifier) istrue , then- Let offsetNs be
ParseTimeZoneOffsetString (systemTimeZoneIdentifier).
- Let offsetNs be
- Else,
- Let offsetNs be
GetNamedTimeZoneOffsetNanoseconds (systemTimeZoneIdentifier,ℤ (ℝ (tv) × 106)).
- Let offsetNs be
- Let offset be
𝔽 (truncate (offsetNs / 106)). - If offset is
+0 𝔽 or offset >+0 𝔽, then- Let offsetSign be
"+" . - Let absOffset be offset.
- Let offsetSign be
- Else,
- Let offsetSign be
"-" . - Let absOffset be -offset.
- Let offsetSign be
- Let offsetMin be
ToZeroPaddedDecimalString (ℝ (MinFromTime (absOffset)), 2). - Let offsetHour be
ToZeroPaddedDecimalString (ℝ (HourFromTime (absOffset)), 2). - Let tzName be an
implementation-defined string that is either the empty String or thestring-concatenation of the code unit 0x0020 (SPACE), the code unit 0x0028 (LEFT PARENTHESIS), animplementation-defined timezone name, and the code unit 0x0029 (RIGHT PARENTHESIS). - Return the
string-concatenation of offsetSign, offsetHour, offsetMin, and tzName.
21.4.4.41.4 ToDateString ( tv )
The abstract operation ToDateString takes argument tv (an
- If tv is
NaN , return"Invalid Date" . - Let t be
LocalTime (tv). - Return the
string-concatenation ofDateString (t), the code unit 0x0020 (SPACE),TimeString (t), andTimeZoneString (tv).
21.4.4.42 Date.prototype.toTimeString ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- If tv is
NaN , return"Invalid Date" . - Let t be
LocalTime (tv). - Return the
string-concatenation ofTimeString (t) andTimeZoneString (tv).
21.4.4.43 Date.prototype.toUTCString ( )
This method returns a String value representing the instant in time corresponding to the
It performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- If tv is
NaN , return"Invalid Date" . - Let weekday be the Name of the entry in
Table 63 with the NumberWeekDay (tv). - Let month be the Name of the entry in
Table 64 with the NumberMonthFromTime (tv). - Let day be
ToZeroPaddedDecimalString (ℝ (DateFromTime (tv)), 2). - Let yv be
YearFromTime (tv). - If yv is
+0 𝔽 or yv >+0 𝔽, let yearSign be the empty String; otherwise, let yearSign be"-" . - Let paddedYear be
ToZeroPaddedDecimalString (abs (ℝ (yv)), 4). - Return the
string-concatenation of weekday,"," , the code unit 0x0020 (SPACE), day, the code unit 0x0020 (SPACE), month, the code unit 0x0020 (SPACE), yearSign, paddedYear, the code unit 0x0020 (SPACE), andTimeString (tv).
21.4.4.44 Date.prototype.valueOf ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Return dateObject.[[DateValue]].
21.4.4.45 Date.prototype [ @@toPrimitive ] ( hint )
This method is called by ECMAScript language operators to convert a Date to a primitive value. The
allowed values for hint are
It performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - If hint is either
"string" or"default" , then- Let tryFirst be
string .
- Let tryFirst be
- Else if hint is
"number" , then- Let tryFirst be
number .
- Let tryFirst be
- Else,
- Throw a
TypeError exception.
- Throw a
- Return ?
OrdinaryToPrimitive (O, tryFirst).
This property has the attributes { [[Writable]]:
The value of the
21.4.5 Properties of Date Instances
Date instances are
22 Text Processing
22.1 String Objects
22.1.1 The String Constructor
The String
- is %String%.
- is the initial value of the
"String" property of theglobal object . - creates and initializes a new String object when called as a
constructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified String behaviour must include asupercall to the Stringconstructor to create and initialize the subclass instance with a [[StringData]] internal slot.
22.1.1.1 String ( value )
This function performs the following steps when called:
- If value is not present, then
- Let s be the empty String.
- Else,
- If NewTarget is
undefined and valueis a Symbol , returnSymbolDescriptiveString (value). - Let s be ?
ToString (value).
- If NewTarget is
- If NewTarget is
undefined , return s. - Return
StringCreate (s, ?GetPrototypeFromConstructor (NewTarget,"%String.prototype%" )).
22.1.2 Properties of the String Constructor
The String
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
22.1.2.1 String.fromCharCode ( ...codeUnits )
This function may be called with any number of arguments which form the rest parameter codeUnits.
It performs the following steps when called:
- Let result be the empty String.
- For each element next of codeUnits, do
- Let nextCU be the code unit whose numeric
value
is
ℝ (?ToUint16 (next)). - Set result to the
string-concatenation of result and nextCU.
- Let nextCU be the code unit whose numeric
value
is
- Return result.
The
22.1.2.2 String.fromCodePoint ( ...codePoints )
This function may be called with any number of arguments which form the rest parameter codePoints.
It performs the following steps when called:
- Let result be the empty String.
- For each element next of codePoints, do
- Let nextCP be ?
ToNumber (next). - If
IsIntegralNumber (nextCP) isfalse , throw aRangeError exception. - If
ℝ (nextCP) < 0 orℝ (nextCP) > 0x10FFFF, throw aRangeError exception. - Set result to the
string-concatenation of result andUTF16EncodeCodePoint (ℝ (nextCP)).
- Let nextCP be ?
Assert : If codePoints is empty, then result is the empty String.- Return result.
The
22.1.2.3 String.prototype
The initial value of String.prototype is the
This property has the attributes { [[Writable]]:
22.1.2.4 String.raw ( template, ...substitutions )
This function may be called with a variable number of arguments. The first argument is
template and the remainder of the arguments form the
It performs the following steps when called:
- Let substitutionCount be the number of elements in substitutions.
- Let cooked be ?
ToObject (template). - Let literals be ?
ToObject (?Get (cooked,"raw" )). - Let literalCount be ?
LengthOfArrayLike (literals). - If literalCount ≤ 0, return the empty String.
- Let R be the empty String.
- Let nextIndex be 0.
- Repeat,
- Let nextLiteralVal be ?
Get (literals, !ToString (𝔽 (nextIndex))). - Let nextLiteral be ?
ToString (nextLiteralVal). - Set R to the
string-concatenation of R and nextLiteral. - If nextIndex + 1 = literalCount, return R.
- If nextIndex <
substitutionCount,
then
- Let nextSubVal be substitutions[nextIndex].
- Let nextSub be ?
ToString (nextSubVal). - Set R to the
string-concatenation of R and nextSub.
- Set nextIndex to nextIndex + 1.
- Let nextLiteralVal be ?
This function is intended for use as a tag function of a Tagged Template (
22.1.3 Properties of the String Prototype Object
The String prototype object:
- is %String.prototype%.
is a String exotic object and has the internal methods specified for such objects.- has a [[StringData]] internal slot whose value is the empty String.
- has a
"length" property whose initial value is+0 𝔽 and whose attributes are { [[Writable]]:false , [[Enumerable]]:false , [[Configurable]]:false }. - has a [[Prototype]] internal slot whose value is
%Object.prototype% .
Unless explicitly stated otherwise, the methods of the String prototype object defined below are not
generic and the
22.1.3.1 String.prototype.at ( index )
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let len be the length of S.
- Let relativeIndex be ?
ToIntegerOrInfinity (index). - If relativeIndex ≥ 0, then
- Let k be relativeIndex.
- Else,
- Let k be len + relativeIndex.
- If k < 0 or k ≥ len,
return
undefined . - Return the
substring of S from k to k + 1.
22.1.3.2 String.prototype.charAt ( pos )
This method returns a single element String containing the code unit at index pos
within
the String value resulting from converting this object to a String. If there is no element at that
index, the result is the empty String. The result
If pos is an x.charAt(pos) is equivalent to the result of
x.substring(pos, pos + 1).
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let position be ?
ToIntegerOrInfinity (pos). - Let size be the length of S.
- If position < 0 or position ≥ size, return the empty String.
- Return the
substring of S from position to position + 1.
This method is intentionally generic; it does not require that its
22.1.3.3 String.prototype.charCodeAt ( pos )
This method returns a Number (a non-negative
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let position be ?
ToIntegerOrInfinity (pos). - Let size be the length of S.
- If position < 0 or position ≥
size, return
NaN . - Return the
Number value for the numeric value of the code unit at index position within the String S.
This method is intentionally generic; it does not require that its
22.1.3.4 String.prototype.codePointAt ( pos )
This method returns a non-negative
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let position be ?
ToIntegerOrInfinity (pos). - Let size be the length of S.
- If position < 0 or position ≥
size, return
undefined . - Let cp be
CodePointAt (S, position). - Return
𝔽 (cp.[[CodePoint]]).
This method is intentionally generic; it does not require that its
22.1.3.5 String.prototype.concat ( ...args )
When this method is called it returns the String value consisting of the code units of the
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let R be S.
- For each element next of args, do
- Let nextString be ?
ToString (next). - Set R to the
string-concatenation of R and nextString.
- Let nextString be ?
- Return R.
The
This method is intentionally generic; it does not require that its
22.1.3.6 String.prototype.constructor
The initial value of String.prototype.constructor is
22.1.3.7 String.prototype.endsWith ( searchString [ , endPosition ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let isRegExp be ?
IsRegExp (searchString). - If isRegExp is
true , throw aTypeError exception. - Let searchStr be ?
ToString (searchString). - Let len be the length of S.
- If endPosition is
undefined , let pos be len; else let pos be ?ToIntegerOrInfinity (endPosition). - Let end be the result of
clamping pos between 0 and len. - Let searchLength be the length of searchStr.
- If searchLength = 0, return
true . - Let start be end - searchLength.
- If start < 0, return
false . - Let substring be the
substring of S from start to end. - If substring is searchStr, return
true . - Return
false .
This method returns
Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
This method is intentionally generic; it does not require that its
22.1.3.8 String.prototype.includes ( searchString [ , position ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let isRegExp be ?
IsRegExp (searchString). - If isRegExp is
true , throw aTypeError exception. - Let searchStr be ?
ToString (searchString). - Let pos be ?
ToIntegerOrInfinity (position). Assert : If position isundefined , then pos is 0.- Let len be the length of S.
- Let start be the result of
clamping pos between 0 and len. - Let index be
StringIndexOf (S, searchStr, start). - If index ≠ -1, return
true . - Return
false .
If searchString appears as a
Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
This method is intentionally generic; it does not require that its
22.1.3.9 String.prototype.indexOf ( searchString [ , position ] )
If searchString appears as a
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let searchStr be ?
ToString (searchString). - Let pos be ?
ToIntegerOrInfinity (position). Assert : If position isundefined , then pos is 0.- Let len be the length of S.
- Let start be the result of
clamping pos between 0 and len. - Return
𝔽 (StringIndexOf (S, searchStr, start)).
This method is intentionally generic; it does not require that its
22.1.3.10 String.prototype.isWellFormed ( )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Return
IsStringWellFormedUnicode (S).
22.1.3.11 String.prototype.lastIndexOf ( searchString [ , position ] )
If searchString appears as a
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let searchStr be ?
ToString (searchString). - Let numPos be ?
ToNumber (position). Assert : If position isundefined , then numPos isNaN .- If numPos is
NaN , let pos be +∞; otherwise, let pos be !ToIntegerOrInfinity (numPos). - Let len be the length of S.
- Let searchLen be the length of searchStr.
- Let start be the result of
clamping pos between 0 and len - searchLen. - If searchStr is the empty String, return
𝔽 (start). - For each
integer i such that 0 ≤ i ≤ start, in descending order, do - Return
-1 𝔽.
This method is intentionally generic; it does not require that its
22.1.3.12 String.prototype.localeCompare ( that [ , reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a Number other than
Before performing the comparisons, this method performs the following steps to prepare the Strings:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let thatValue be ?
ToString (that).
The meaning of the optional second and third parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not assign any other interpretation to those parameter positions.
The actual return values are
This method itself is not directly suitable as an argument to Array.prototype.sort
because the latter requires a function of two arguments.
This method may rely on whatever language- and/or locale-sensitive comparison functionality is
available to the ECMAScript environment from the
// Å ANGSTROM SIGN vs.
// Å LATIN CAPITAL LETTER A + COMBINING RING ABOVE
"\u212B".localeCompare("A\u030A")
// Ω OHM SIGN vs.
// Ω GREEK CAPITAL LETTER OMEGA
"\u2126".localeCompare("\u03A9")
// ṩ LATIN SMALL LETTER S WITH DOT BELOW AND DOT ABOVE vs.
// ṩ LATIN SMALL LETTER S + COMBINING DOT ABOVE + COMBINING DOT BELOW
"\u1E69".localeCompare("s\u0307\u0323")
// ḍ̇ LATIN SMALL LETTER D WITH DOT ABOVE + COMBINING DOT BELOW vs.
// ḍ̇ LATIN SMALL LETTER D WITH DOT BELOW + COMBINING DOT ABOVE
"\u1E0B\u0323".localeCompare("\u1E0D\u0307")
// 가 HANGUL CHOSEONG KIYEOK + HANGUL JUNGSEONG A vs.
// 가 HANGUL SYLLABLE GA
"\u1100\u1161".localeCompare("\uAC00")For a definition and discussion of canonical equivalence see the Unicode Standard, chapters 2 and 3, as well as Unicode Standard Annex #15, Unicode Normalization Forms and Unicode Technical Note #5, Canonical Equivalence in Applications. Also see Unicode Technical Standard #10, Unicode Collation Algorithm.
It is recommended that this method should not honour Unicode compatibility equivalents or compatibility decompositions as defined in the Unicode Standard, chapter 3, section 3.7.
This method is intentionally generic; it does not require that its
22.1.3.13 String.prototype.match ( regexp )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If regexp is neither
undefined nornull , then - Let S be ?
ToString (O). - Let rx be ?
RegExpCreate (regexp,undefined ). - Return ?
Invoke (rx,@@match , « S »).
This method is intentionally generic; it does not require that its
22.1.3.14 String.prototype.matchAll ( regexp )
This method performs a regular expression match of the String representing the
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If regexp is neither
undefined nornull , then- Let isRegExp be ?
IsRegExp (regexp). - If isRegExp is
true , then- Let flags be ?
Get (regexp,"flags" ). - Perform ?
RequireObjectCoercible (flags). - If ?
ToString (flags) does not contain"g" , throw aTypeError exception.
- Let flags be ?
- Let matcher be ?
GetMethod (regexp,@@matchAll ). - If matcher is not
undefined , then- Return ?
Call (matcher, regexp, « O »).
- Return ?
- Let isRegExp be ?
- Let S be ?
ToString (O). - Let rx be ?
RegExpCreate (regexp,"g" ). - Return ?
Invoke (rx,@@matchAll , « S »).
String.prototype.split,
String.prototype.matchAll is designed to typically act without mutating its inputs.
22.1.3.15 String.prototype.normalize ( [ form ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - If form is
undefined , let f be"NFC" . - Else, let f be ?
ToString (form). - If f is not one of
"NFC" ,"NFD" ,"NFKC" , or"NFKD" , throw aRangeError exception. - Let ns be the String value that is the result of normalizing S into the normalization form named by f as specified in the latest Unicode Standard, Normalization Forms.
- Return ns.
This method is intentionally generic; it does not require that its
22.1.3.16 String.prototype.padEnd ( maxLength [ , fillString ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Return ?
StringPaddingBuiltinsImpl (O, maxLength, fillString,end ).
22.1.3.17 String.prototype.padStart ( maxLength [ , fillString ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Return ?
StringPaddingBuiltinsImpl (O, maxLength, fillString,start ).
22.1.3.17.1 StringPaddingBuiltinsImpl ( O, maxLength, fillString, placement )
The abstract operation StringPaddingBuiltinsImpl takes arguments O (an
- Let S be ?
ToString (O). - Let intMaxLength be
ℝ (?ToLength (maxLength)). - Let stringLength be the length of S.
- If intMaxLength ≤ stringLength, return S.
- If fillString is
undefined , set fillString to the String value consisting solely of the code unit 0x0020 (SPACE). - Else, set fillString to ?
ToString (fillString). - Return
StringPad (S, intMaxLength, fillString, placement).
22.1.3.17.2 StringPad ( S, maxLength, fillString, placement )
The abstract operation StringPad takes arguments S (a String), maxLength (a
non-negative
- Let stringLength be the length of S.
- If maxLength ≤ stringLength, return S.
- If fillString is the empty String, return S.
- Let fillLen be maxLength - stringLength.
- Let truncatedStringFiller be the String value consisting of repeated concatenations of fillString truncated to length fillLen.
- If placement is
start , return thestring-concatenation of truncatedStringFiller and S. - Else, return the
string-concatenation of S and truncatedStringFiller.
The argument maxLength will be clamped such that it can be no smaller than the length of S.
The argument fillString defaults to
22.1.3.17.3 ToZeroPaddedDecimalString ( n, minLength )
The abstract operation ToZeroPaddedDecimalString takes arguments n (a non-negative
- Let S be the String representation of n, formatted as a decimal number.
- Return
StringPad (S, minLength,"0" ,start ).
22.1.3.18 String.prototype.repeat ( count )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let n be ?
ToIntegerOrInfinity (count). - If n < 0 or n = +∞, throw a
RangeError exception. - If n = 0, return the empty String.
- Return the String value that is made from n copies of S appended together.
This method creates the String value consisting of the code units of the
This method is intentionally generic; it does not require that its
22.1.3.19 String.prototype.replace ( searchValue, replaceValue )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If searchValue is neither
undefined nornull , then - Let string be ?
ToString (O). - Let searchString be ?
ToString (searchValue). - Let functionalReplace be
IsCallable (replaceValue). - If functionalReplace is
false , then- Set replaceValue to ?
ToString (replaceValue).
- Set replaceValue to ?
- Let searchLength be the length of searchString.
- Let position be
StringIndexOf (string, searchString, 0). - If position = -1, return string.
- Let preceding be the
substring of string from 0 to position. - Let following be the
substring of string from position + searchLength. - If functionalReplace is
true , then - Else,
Assert : replaceValueis a String .- Let captures be a new empty
List . - Let replacement be !
GetSubstitution (searchString, string, position, captures,undefined , replaceValue).
- Return the
string-concatenation of preceding, replacement, and following.
This method is intentionally generic; it does not require that its
22.1.3.19.1 GetSubstitution ( matched, str, position, captures, namedCaptures, replacementTemplate )
The abstract operation GetSubstitution takes arguments matched (a String),
str
(a
String), position (a non-negative
- Let stringLength be the length of str.
Assert : position ≤ stringLength.- Let result be the empty String.
- Let templateRemainder be replacementTemplate.
- Repeat, while templateRemainder is not the empty
String,
- NOTE: The following steps isolate ref (a prefix of templateRemainder), determine refReplacement (its replacement), and then append that replacement to result.
- If templateRemainder starts with
"$$" , then- Let ref be
"$$" . - Let refReplacement be
"$" .
- Let ref be
- Else if templateRemainder starts with
"$`" , then- Let ref be
"$`" . - Let refReplacement be the
substring of str from 0 to position.
- Let ref be
- Else if templateRemainder starts with
"$&" , then- Let ref be
"$&" . - Let refReplacement be matched.
- Let ref be
- Else if templateRemainder starts with
"$'" (0x0024 (DOLLAR SIGN) followed by 0x0027 (APOSTROPHE)), then- Let ref be
"$'" . - Let matchLength be the length of matched.
- Let tailPos be position + matchLength.
- Let refReplacement be the
substring of str frommin (tailPos, stringLength). - NOTE: tailPos can exceed
stringLength only if this abstract operation was invoked by a call to the
intrinsic
@@replace method of%RegExp.prototype% on an object whose"exec" property is not the intrinsic %RegExp.prototype.exec%.
- Let ref be
- Else if templateRemainder starts with
"$" followed by 1 or more decimal digits, then- If templateRemainder starts with
"$" followed by 2 or more decimal digits, let digitCount be 2. Otherwise, let digitCount be 1. - Let digits be the
substring of templateRemainder from 1 to 1 + digitCount. - Let index be
ℝ (StringToNumber (digits)). Assert : 0 ≤ index ≤ 99.- Let captureLen be the number of elements in captures.
- If index > captureLen and
digitCount = 2, then
- NOTE: When a two-digit replacement pattern specifies an index exceeding the count of capturing groups, it is treated as a one-digit replacement pattern followed by a literal digit.
- Set digitCount to 1.
- Set digits to the
substring of digits from 0 to 1. - Set index to
ℝ (StringToNumber (digits)).
- Let ref be the
substring of templateRemainder from 0 to 1 + digitCount. - If 1 ≤ index ≤ captureLen,
then
- Let capture be captures[index - 1].
- If capture is
undefined , then- Let refReplacement be the empty String.
- Else,
- Let refReplacement be capture.
- Else,
- Let refReplacement be ref.
- If templateRemainder starts with
- Else if templateRemainder starts with
"$<" , then- Let gtPos be
StringIndexOf (templateRemainder,">" , 0). - If gtPos = -1 or
namedCaptures
is
undefined , then- Let ref be
"$<" . - Let refReplacement be ref.
- Let ref be
- Else,
- Let ref be the
substring of templateRemainder from 0 to gtPos + 1. - Let groupName be the
substring of templateRemainder from 2 to gtPos. Assert : namedCapturesis an Object .- Let capture be ?
Get (namedCaptures, groupName). - If capture is
undefined , then- Let refReplacement be the empty String.
- Else,
- Let refReplacement be
?
ToString (capture).
- Let refReplacement be
?
- Let ref be the
- Let gtPos be
- Else,
- Let ref be the
substring of templateRemainder from 0 to 1. - Let refReplacement be ref.
- Let ref be the
- Let refLength be the length of ref.
- Set templateRemainder to the
substring of templateRemainder from refLength. - Set result to the
string-concatenation of result and refReplacement.
- Return result.
22.1.3.20 String.prototype.replaceAll ( searchValue, replaceValue )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If searchValue is neither
undefined nornull , then- Let isRegExp be ?
IsRegExp (searchValue). - If isRegExp is
true , then- Let flags be ?
Get (searchValue,"flags" ). - Perform ?
RequireObjectCoercible (flags). - If ?
ToString (flags) does not contain"g" , throw aTypeError exception.
- Let flags be ?
- Let replacer be ?
GetMethod (searchValue,@@replace ). - If replacer is not
undefined , then- Return ?
Call (replacer, searchValue, « O, replaceValue »).
- Return ?
- Let isRegExp be ?
- Let string be ?
ToString (O). - Let searchString be ?
ToString (searchValue). - Let functionalReplace be
IsCallable (replaceValue). - If functionalReplace is
false , then- Set replaceValue to ?
ToString (replaceValue).
- Set replaceValue to ?
- Let searchLength be the length of searchString.
- Let advanceBy be
max (1, searchLength). - Let matchPositions be a new empty
List . - Let position be
StringIndexOf (string, searchString, 0). - Repeat, while position ≠ -1,
- Append position to matchPositions.
- Set position to
StringIndexOf (string, searchString, position + advanceBy).
- Let endOfLastMatch be 0.
- Let result be the empty String.
- For each element p of matchPositions,
do
- Let preserved be the
substring of string from endOfLastMatch to p. - If functionalReplace is
true , then - Else,
Assert : replaceValueis a String .- Let captures be a new empty
List . - Let replacement be !
GetSubstitution (searchString, string, p, captures,undefined , replaceValue).
- Set result to the
string-concatenation of result, preserved, and replacement. - Set endOfLastMatch to p + searchLength.
- Let preserved be the
- If endOfLastMatch < the length of
string, then
- Set result to the
string-concatenation of result and thesubstring of string from endOfLastMatch.
- Set result to the
- Return result.
22.1.3.21 String.prototype.search ( regexp )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If regexp is neither
undefined nornull , then - Let string be ?
ToString (O). - Let rx be ?
RegExpCreate (regexp,undefined ). - Return ?
Invoke (rx,@@search , « string »).
This method is intentionally generic; it does not require that its
22.1.3.22 String.prototype.slice ( start, end )
This method returns a
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let len be the length of S.
- Let intStart be ?
ToIntegerOrInfinity (start). - If intStart = -∞, let from be 0.
- Else if intStart < 0, let from be
max (len + intStart, 0). - Else, let from be
min (intStart, len). - If end is
undefined , let intEnd be len; else let intEnd be ?ToIntegerOrInfinity (end). - If intEnd = -∞, let to be 0.
- Else if intEnd < 0, let to be
max (len + intEnd, 0). - Else, let to be
min (intEnd, len). - If from ≥ to, return the empty String.
- Return the
substring of S from from to to.
This method is intentionally generic; it does not require that its
22.1.3.23 String.prototype.split ( separator, limit )
This method returns an Array into which substrings of the result of converting this object to a
String
have been stored. The substrings are determined by searching from left to right for occurrences of
separator; these occurrences are not part of any String in the returned array, but serve to
divide up the String value. The value of separator may be a String of any length or it may
be
an object, such as a RegExp, that has a
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If separator is neither
undefined nornull , then - Let S be ?
ToString (O). - If limit is
undefined , let lim be 232 - 1; else let lim beℝ (?ToUint32 (limit)). - Let R be ?
ToString (separator). - If lim = 0, then
- Return
CreateArrayFromList (« »).
- Return
- If separator is
undefined , then- Return
CreateArrayFromList (« S »).
- Return
- Let separatorLength be the length of R.
- If separatorLength = 0, then
- Let head be the
substring of S from 0 to lim. - Let codeUnits be a
List consisting of the sequence of code units that are the elements of head. - Return
CreateArrayFromList (codeUnits).
- Let head be the
- If S is the empty String, return
CreateArrayFromList (« S »). - Let substrings be a new empty
List . - Let i be 0.
- Let j be
StringIndexOf (S, R, 0). - Repeat, while j ≠ -1,
- Let T be the
substring of S from i to j. - Append T to substrings.
- If the number of elements in substrings is
lim, return
CreateArrayFromList (substrings). - Set i to j + separatorLength.
- Set j to
StringIndexOf (S, R, i).
- Let T be the
- Let T be the
substring of S from i. - Append T to substrings.
- Return
CreateArrayFromList (substrings).
The value of separator may be an empty String. In this case, separator does
not
match the empty
If the
If separator is
This method is intentionally generic; it does not require that its
22.1.3.24 String.prototype.startsWith ( searchString [ , position ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let isRegExp be ?
IsRegExp (searchString). - If isRegExp is
true , throw aTypeError exception. - Let searchStr be ?
ToString (searchString). - Let len be the length of S.
- If position is
undefined , let pos be 0; else let pos be ?ToIntegerOrInfinity (position). - Let start be the result of
clamping pos between 0 and len. - Let searchLength be the length of searchStr.
- If searchLength = 0, return
true . - Let end be start + searchLength.
- If end > len, return
false . - Let substring be the
substring of S from start to end. - If substring is searchStr, return
true . - Return
false .
This method returns
Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
This method is intentionally generic; it does not require that its
22.1.3.25 String.prototype.substring ( start, end )
This method returns a
If either argument is
If start is strictly greater than end, they are swapped.
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let len be the length of S.
- Let intStart be ?
ToIntegerOrInfinity (start). - If end is
undefined , let intEnd be len; else let intEnd be ?ToIntegerOrInfinity (end). - Let finalStart be the result of
clamping intStart between 0 and len. - Let finalEnd be the result of
clamping intEnd between 0 and len. - Let from be
min (finalStart, finalEnd). - Let to be
max (finalStart, finalEnd). - Return the
substring of S from from to to.
This method is intentionally generic; it does not require that its
22.1.3.26 String.prototype.toLocaleLowerCase ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It works exactly the same as toLowerCase except that it is intended to yield a
locale-sensitive result corresponding with conventions of the
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
This method is intentionally generic; it does not require that its
22.1.3.27 String.prototype.toLocaleUpperCase ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It works exactly the same as toUpperCase except that it is intended to yield a
locale-sensitive result corresponding with conventions of the
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
This method is intentionally generic; it does not require that its
22.1.3.28 String.prototype.toLowerCase ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let sText be
StringToCodePoints (S). - Let lowerText be the result of toLowercase(sText), according to the Unicode Default Case Conversion algorithm.
- Let L be
CodePointsToString (lowerText). - Return L.
The result must be derived according to the locale-insensitive case mappings in the Unicode Character
Database (this explicitly includes not only the file UnicodeData.txt,
but
also all locale-insensitive mappings in the file SpecialCasing.txt
that accompanies it).
The case mapping of some code points may produce multiple code points. In this case the result
String
may not be the same length as the source String. Because both toUpperCase and
toLowerCase have context-sensitive behaviour, the methods are not symmetrical. In
other
words, s.toUpperCase().toLowerCase() is not necessarily equal to
s.toLowerCase().
This method is intentionally generic; it does not require that its
22.1.3.29 String.prototype.toString ( )
This method performs the following steps when called:
- Return ?
ThisStringValue (this value).
For a String object, this method happens to return the same thing as the valueOf
method.
22.1.3.30 String.prototype.toUpperCase ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It behaves in exactly the same way as String.prototype.toLowerCase, except that the
String
is mapped using the toUppercase algorithm of the Unicode Default Case Conversion.
This method is intentionally generic; it does not require that its
22.1.3.31 String.prototype.toWellFormed ( )
This method returns a String representation of this object with all
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let strLen be the length of S.
- Let k be 0.
- Let result be the empty String.
- Repeat, while k < strLen,
- Let cp be
CodePointAt (S, k). - If cp.[[IsUnpairedSurrogate]] is
true , then- Set result to the
string-concatenation of result and 0xFFFD (REPLACEMENT CHARACTER).
- Set result to the
- Else,
- Set result to the
string-concatenation of result andUTF16EncodeCodePoint (cp.[[CodePoint]]).
- Set result to the
- Set k to k + cp.[[CodeUnitCount]].
- Let cp be
- Return result.
22.1.3.32 String.prototype.trim ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It performs the following steps when called:
- Let S be the
this value. - Return ?
TrimString (S,start+end ).
This method is intentionally generic; it does not require that its
22.1.3.32.1 TrimString ( string, where )
The abstract operation TrimString takes arguments string (an
- Let str be ?
RequireObjectCoercible (string). - Let S be ?
ToString (str). - If where is
start , then- Let T be the String value that is a copy of S with leading white space removed.
- Else if where is
end , then- Let T be the String value that is a copy of S with trailing white space removed.
- Else,
Assert : where isstart+end .- Let T be the String value that is a copy of S with both leading and trailing white space removed.
- Return T.
The definition of white space is the union of
22.1.3.33 String.prototype.trimEnd ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It performs the following steps when called:
- Let S be the
this value. - Return ?
TrimString (S,end ).
This method is intentionally generic; it does not require that its
22.1.3.34 String.prototype.trimStart ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It performs the following steps when called:
- Let S be the
this value. - Return ?
TrimString (S,start ).
This method is intentionally generic; it does not require that its
22.1.3.35 String.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ThisStringValue (this value).
22.1.3.35.1 ThisStringValue ( value )
The abstract operation ThisStringValue takes argument value (an
- If value
is a String , return value. - If value
is an Object and value has a [[StringData]] internal slot, then- Let s be value.[[StringData]].
Assert : sis a String .- Return s.
- Throw a
TypeError exception.
22.1.3.36 String.prototype [ @@iterator ] ( )
This method returns an Iterator object (
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let s be ?
ToString (O). - Let closure be a new
Abstract Closure with no parameters that captures s and performs the following steps when called:- Let len be the length of s.
- Let position be 0.
- Repeat, while position < len,
- Let cp be
CodePointAt (s, position). - Let nextIndex be position + cp.[[CodeUnitCount]].
- Let resultString be the
substring of s from position to nextIndex. - Set position to nextIndex.
- Perform ?
GeneratorYield (CreateIterResultObject (resultString,false )).
- Let cp be
- Return
undefined .
- Return
CreateIteratorFromClosure (closure,"%StringIteratorPrototype%" ,%StringIteratorPrototype% ).
The value of the
22.1.4 Properties of String Instances
String instances are
String instances have a
22.1.4.1 length
The number of elements in the String value represented by this String object.
Once a String object is initialized, this property is unchanging. It has the attributes { [[Writable]]:
22.1.5 String Iterator Objects
A String Iterator is an object, that represents a specific iteration over some specific String instance
object. There is not a named
22.1.5.1 The %StringIteratorPrototype% Object
The %StringIteratorPrototype% object:
- has properties that are inherited by all String Iterator Objects.
- is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%IteratorPrototype% . - has the following properties:
22.1.5.1.1 %StringIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%StringIteratorPrototype%" ).
22.1.5.1.2 %StringIteratorPrototype% [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
22.2 RegExp (Regular Expression) Objects
A RegExp object contains a regular expression and the associated flags.
The form and functionality of regular expressions is modelled after the regular expression facility in the Perl 5 programming language.
22.2.1 Patterns
The RegExp
Syntax
Each \u u u \u
The first two lines here are equivalent to CharacterClass.
A number of productions in this section are given alternative definitions in section
22.2.1.1 Static Semantics: Early Errors
This section is amended in
-
It is a Syntax Error if
CountLeftCapturingParensWithin (Pattern ) ≥ 232 - 1. -
It is a Syntax Error if
Pattern contains two or moreGroupSpecifier s for whichCapturingGroupName ofGroupSpecifier is the same.
-
It is a Syntax Error if the MV of the first
DecimalDigits is strictly greater than the MV of the secondDecimalDigits .
-
It is a Syntax Error if
GroupSpecifiersThatMatch (GroupName ) is empty.
-
It is a Syntax Error if the
CapturingGroupNumber ofDecimalEscape is strictly greater thanCountLeftCapturingParensWithin (thePattern containingAtomEscape ).
-
It is a Syntax Error if
IsCharacterClass of the firstClassAtom istrue orIsCharacterClass of the secondClassAtom istrue . -
It is a Syntax Error if
IsCharacterClass of the firstClassAtom isfalse ,IsCharacterClass of the secondClassAtom isfalse , and theCharacterValue of the firstClassAtom is strictly greater than theCharacterValue of the secondClassAtom .
-
It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash istrue orIsCharacterClass ofClassAtom istrue . -
It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash isfalse ,IsCharacterClass ofClassAtom isfalse , and theCharacterValue ofClassAtomNoDash is strictly greater than theCharacterValue ofClassAtom .
-
It is a Syntax Error if the
CharacterValue ofRegExpUnicodeEscapeSequence is not the numeric value of some code point matched by theIdentifierStartChar lexical grammar production.
-
It is a Syntax Error if
RegExpIdentifierCodePoint ofRegExpIdentifierStart is not matched by theUnicodeIDStart lexical grammar production.
-
It is a Syntax Error if the
CharacterValue ofRegExpUnicodeEscapeSequence is not the numeric value of some code point matched by theIdentifierPartChar lexical grammar production.
-
It is a Syntax Error if
RegExpIdentifierCodePoint ofRegExpIdentifierPart is not matched by theUnicodeIDContinue lexical grammar production.
-
It is a Syntax Error if the
source text matched by UnicodePropertyName is not a Unicodeproperty name or property alias listed in the “Property name and aliases” column ofTable 67 . -
It is a Syntax Error if the
source text matched by UnicodePropertyValue is not a property value or property value alias for the Unicode property or property alias given by thesource text matched by UnicodePropertyName listed inPropertyValueAliases.txt.
-
It is a Syntax Error if the
source text matched by LoneUnicodePropertyNameOrValue is not a Unicode property value or property value alias for the General_Category (gc) property listed inPropertyValueAliases.txt, nor a binary property or binary property alias listed in the “Property name and aliases” column ofTable 68 , nor a binary property of strings listed in the “Property name ” column ofTable 69 . -
It is a Syntax Error if the enclosing
Pattern does not have a [UnicodeSetsMode] parameter and thesource text matched by LoneUnicodePropertyNameOrValue is a binary property of strings listed in the “Property name ” column ofTable 69 .
-
It is a Syntax Error if
MayContainStrings of theUnicodePropertyValueExpression istrue .
-
It is a Syntax Error if
MayContainStrings of theClassContents istrue .
-
It is a Syntax Error if
MayContainStrings of theClassContents istrue .
-
It is a Syntax Error if the
CharacterValue of the firstClassSetCharacter is strictly greater than theCharacterValue of the secondClassSetCharacter .
22.2.1.2 Static Semantics: CountLeftCapturingParensWithin ( node )
The abstract operation CountLeftCapturingParensWithin takes argument node (a ( pattern character that is
matched
by the ( terminal of the
This section is amended in
It performs the following steps when called:
Assert : node is an instance of a production inthe RegExp Pattern grammar .- Return the number of
Atom :: ( GroupSpecifier opt Disjunction ) Parse Nodes contained within node.
22.2.1.3 Static Semantics: CountLeftCapturingParensBefore ( node )
The abstract operation CountLeftCapturingParensBefore takes argument node (a
This section is amended in
It performs the following steps when called:
Assert : node is an instance of a production inthe RegExp Pattern grammar .- Let pattern be the
Pattern containing node. - Return the number of
Atom :: ( GroupSpecifier opt Disjunction ) Parse Nodes contained within pattern that either occur before node or contain node.
22.2.1.4 Static Semantics: CapturingGroupNumber
The
This section is amended in
It is defined piecewise over the following productions:
- Return the MV of
NonZeroDigit .
- Let n be the number of code points in
DecimalDigits . - Return (the MV of
NonZeroDigit × 10n plus the MV ofDecimalDigits ).
The definitions of “the MV of
22.2.1.5 Static Semantics: IsCharacterClass
The
This section is amended in
It is defined piecewise over the following productions:
- Return
false .
- Return
true .
22.2.1.6 Static Semantics: CharacterValue
The
This section is amended in
It is defined piecewise over the following productions:
- Return the numeric value of U+002D (HYPHEN-MINUS).
- Let ch be the code point matched by
SourceCharacter . - Return the numeric value of ch.
- Return the numeric value of U+0008 (BACKSPACE).
- Return the numeric value of U+002D (HYPHEN-MINUS).
- Return the numeric value according to
Table 65 .
| ControlEscape | Numeric Value | Code Point | Unicode Name | Symbol |
|---|---|---|---|---|
t
|
9 |
U+0009
|
CHARACTER TABULATION | <HT> |
n
|
10 |
U+000A
|
LINE FEED (LF) | <LF> |
v
|
11 |
U+000B
|
LINE TABULATION | <VT> |
f
|
12 |
U+000C
|
FORM FEED (FF) | <FF> |
r
|
13 |
U+000D
|
CARRIAGE RETURN (CR) | <CR> |
- Let ch be the code point matched by
AsciiLetter . - Let i be the numeric value of ch.
- Return the remainder of dividing i by 32.
- Return the numeric value of U+0000 (NULL).
\0 represents the <NUL> character and cannot be followed by a decimal digit.
- Return the MV of
HexEscapeSequence .
- Let lead be the
CharacterValue ofHexLeadSurrogate . - Let trail be the
CharacterValue ofHexTrailSurrogate . - Let cp be
UTF16SurrogatePairToCodePoint (lead, trail). - Return the numeric value of cp.
- Return the MV of
Hex4Digits .
- Return the MV of
CodePoint .
- Return the MV of
Hex4Digits .
- Let ch be the code point matched by
IdentityEscape . - Return the numeric value of ch.
- Let ch be the code point matched by
SourceCharacter . - Return the numeric value of ch.
- Let ch be the code point matched by
ClassSetReservedPunctuator . - Return the numeric value of ch.
- Return the numeric value of U+0008 (BACKSPACE).
22.2.1.7 Static Semantics: MayContainStrings
The
- Return
false .
- If the
source text matched by LoneUnicodePropertyNameOrValue is a binary property of strings listed in the “Property name ” column ofTable 69 , returntrue . - Return
false .
- If the
ClassUnion is present, returnMayContainStrings of theClassUnion . - Return
false .
- If
MayContainStrings of theClassSetOperand istrue , returntrue . - If
ClassUnion is present, returnMayContainStrings of theClassUnion . - Return
false .
- If
MayContainStrings of the firstClassSetOperand isfalse , returnfalse . - If
MayContainStrings of the secondClassSetOperand isfalse , returnfalse . - Return
true .
- If
MayContainStrings of theClassIntersection isfalse , returnfalse . - If
MayContainStrings of theClassSetOperand isfalse , returnfalse . - Return
true .
- Return
MayContainStrings of the firstClassSetOperand .
- Return
MayContainStrings of theClassSubtraction .
- If
MayContainStrings of theClassString istrue , returntrue . - Return
MayContainStrings of theClassStringDisjunctionContents .
- Return
true .
- Return
MayContainStrings of theNonEmptyClassString .
- If
NonEmptyClassString is present, returntrue . - Return
false .
22.2.1.8 Static Semantics: GroupSpecifiersThatMatch ( thisGroupName )
The abstract operation GroupSpecifiersThatMatch takes argument thisGroupName (a
- Let name be the
CapturingGroupName of thisGroupName. - Let pattern be the
Pattern containing thisGroupName. - Let result be a new empty
List . - For each
GroupSpecifier gs that pattern contains, do- If the
CapturingGroupName of gs is name, then- Append gs to result.
- If the
- Return result.
22.2.1.9 Static Semantics: CapturingGroupName
The
- Let idTextUnescaped be
RegExpIdentifierCodePoints ofRegExpIdentifierName . - Return
CodePointsToString (idTextUnescaped).
22.2.1.10 Static Semantics: RegExpIdentifierCodePoints
The
- Let cp be
RegExpIdentifierCodePoint ofRegExpIdentifierStart . - Return « cp ».
- Let cps be
RegExpIdentifierCodePoints of the derivedRegExpIdentifierName . - Let cp be
RegExpIdentifierCodePoint ofRegExpIdentifierPart . - Return the
list-concatenation of cps and « cp ».
22.2.1.11 Static Semantics: RegExpIdentifierCodePoint
The
- Return the code point matched by
IdentifierStartChar .
- Return the code point matched by
IdentifierPartChar .
- Return the code point whose numeric value is the
CharacterValue ofRegExpUnicodeEscapeSequence .
- Let lead be the code unit whose numeric value is
the
numeric value of the code point matched by
UnicodeLeadSurrogate . - Let trail be the code unit whose numeric value is
the
numeric value of the code point matched by
UnicodeTrailSurrogate . - Return
UTF16SurrogatePairToCodePoint (lead, trail).
22.2.2 Pattern Semantics
A regular expression pattern is converted into an
A u nor a v. Otherwise, it
is
a Unicode pattern. A BMP pattern matches against a String interpreted as consisting of a sequence of
16-bit
values that are Unicode code points in the range of the Basic Multilingual Plane. A Unicode pattern
matches
against a String interpreted as consisting of Unicode code points encoded using UTF-16. In the context
of
describing the behaviour of a BMP pattern “character” means a single 16-bit Unicode BMP code point. In
the
context of describing the behaviour of a Unicode pattern “character” means a UTF-16 encoded code point
(
The syntax and semantics of
For example, consider a pattern expressed in source text as the single non-BMP character U+1D11E
(MUSICAL SYMBOL G CLEF). Interpreted as a Unicode pattern, it would be a single element (character)
Patterns are passed to the RegExp
An implementation may not actually perform such translations to or from UTF-16, but the semantics of this specification requires that the result of pattern matching be as if such translations were performed.
22.2.2.1 Notation
The descriptions below use the following internal data structures:
-
A CharSetElement is one of the two following entities:
-
If rer.[[UnicodeSets]] is
false , then a CharSetElement is a character in the sense of the Pattern Semantics above. -
If rer.[[UnicodeSets]] is
true , then a CharSetElement is a sequence whose elements are characters in the sense of the Pattern Semantics above. This includes the empty sequence, sequences of one character, and sequences of more than one character. For convenience, when working with CharSetElements of this kind, an individual character is treated interchangeably with a sequence of one character.
-
If rer.[[UnicodeSets]] is
- A CharSet is a mathematical set of CharSetElements.
-
A CaptureRange is a
Record { [[StartIndex]], [[EndIndex]] } that represents the range of characters included in a capture, where [[StartIndex]] is aninteger representing the start index (inclusive) of the range within Input, and [[EndIndex]] is aninteger representing the end index (exclusive) of the range within Input. For anyCaptureRange , these indices must satisfy the invariant that [[StartIndex]] ≤ [[EndIndex]]. -
A MatchState is a
Record { [[Input]], [[EndIndex]], [[Captures]] } where [[Input]] is aList of characters representing the String being matched, [[EndIndex]] is aninteger , and [[Captures]] is aList of values, one for eachleft-capturing parenthesis in the pattern. States are used to represent partial match states in the regular expression matching algorithms. The [[EndIndex]] is one plus the index of the last input character matched so far by the pattern, while [[Captures]] holds the results of capturing parentheses. The nth element of [[Captures]] is either aCaptureRange representing the range of characters captured by the nth set of capturing parentheses, orundefined if the nth set of capturing parentheses hasn't been reached yet. Due to backtracking, many States may be in use at any time during the matching process. -
A MatchResult is either a
MatchState or the special tokenfailure that indicates that the match failed. -
A MatcherContinuation is an
Abstract Closure that takes oneMatchState argument and returns aMatchResult result. TheMatcherContinuation attempts to match the remaining portion (specified by the closure's captured values) of the pattern against Input, starting at the intermediate state given by itsMatchState argument. If the match succeeds, theMatcherContinuation returns the finalMatchState that it reached; if the match fails, theMatcherContinuation returnsfailure . -
A Matcher is an
Abstract Closure that takes two arguments—aMatchState and aMatcherContinuation —and returns aMatchResult result. AMatcher attempts to match a middle subpattern (specified by the closure's captured values) of the pattern against theMatchState 's [[Input]], starting at the intermediate state given by itsMatchState argument. TheMatcherContinuation argument should be a closure that matches the rest of the pattern. After matching the subpattern of a pattern to obtain a newMatchState , theMatcher then callsMatcherContinuation on that newMatchState to test if the rest of the pattern can match as well. If it can, theMatcher returns theMatchState returned byMatcherContinuation ; if not, theMatcher may try different choices at its choice points, repeatedly callingMatcherContinuation until it either succeeds or all possibilities have been exhausted.
22.2.2.1.1 RegExp Records
A RegExp Record is a
It has the following fields:
| Field Name | Value | Meaning |
|---|---|---|
| [[IgnoreCase]] | a Boolean | indicates whether |
| [[Multiline]] | a Boolean | indicates whether |
| [[DotAll]] | a Boolean | indicates whether |
| [[Unicode]] | a Boolean | indicates whether |
| [[UnicodeSets]] | a Boolean | indicates whether |
| [[CapturingGroupsCount]] | a non-negative |
the number of |
22.2.2.2 Runtime Semantics: CompilePattern
The
- Let m be
CompileSubpattern ofDisjunction with arguments rer andforward . - Return a new
Abstract Closure with parameters (Input, index) that captures rer and m and performs the following steps when called:Assert : Input is aList of characters.Assert : 0 ≤ index ≤ the number of elements in Input.- Let c be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let cap be a
List of rer.[[CapturingGroupsCount]]undefined values, indexed 1 through rer.[[CapturingGroupsCount]]. - Let x be the
MatchState { [[Input]]: Input, [[EndIndex]]: index, [[Captures]]: cap }. - Return m(x, c).
A Pattern compiles to an
22.2.2.3 Runtime Semantics: CompileSubpattern
The
This section is amended in
It is defined piecewise over the following productions:
- Let m1 be
CompileSubpattern ofAlternative with arguments rer and direction. - Let m2 be
CompileSubpattern ofDisjunction with arguments rer and direction. - Return
MatchTwoAlternatives (m1, m2).
The | regular expression operator separates two alternatives. The pattern first
tries
to
match the left | produce
/a|ab/.exec("abc")returns the result
/((a)|(ab))((c)|(bc))/.exec("abc")returns the array
["abc", "a", "a", undefined, "bc", undefined, "bc"]and not
["abc", "ab", undefined, "ab", "c", "c", undefined]The order in which the two alternatives are tried is independent of the value of direction.
- Return
EmptyMatcher ().
- Let m1 be
CompileSubpattern ofAlternative with arguments rer and direction. - Let m2 be
CompileSubpattern ofTerm with arguments rer and direction. - Return
MatchSequence (m1, m2, direction).
Consecutive
- Return
CompileAssertion ofAssertion with argument rer.
The resulting
- Return
CompileAtom ofAtom with arguments rer and direction.
- Let m be
CompileAtom ofAtom with arguments rer and direction. - Let q be
CompileQuantifier ofQuantifier . Assert : q.[[Min]] ≤ q.[[Max]].- Let parenIndex be
CountLeftCapturingParensBefore (Term ). - Let parenCount be
CountLeftCapturingParensWithin (Atom ). - Return a new
Matcher with parameters (x, c) that captures m, q, parenIndex, and parenCount and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Return
RepeatMatcher (m, q.[[Min]], q.[[Max]], q.[[Greedy]], x, c, parenIndex, parenCount).
22.2.2.3.1 RepeatMatcher ( m, min, max, greedy, x, c, parenIndex, parenCount )
The abstract operation RepeatMatcher takes arguments m (a
- If max = 0, return c(x).
- Let d be a new
MatcherContinuation with parameters (y) that captures m, min, max, greedy, x, c, parenIndex, and parenCount and performs the following steps when called:Assert : y is aMatchState .- If min = 0 and
y.[[EndIndex]] = x.[[EndIndex]], return
failure . - If min = 0, let min2 be 0; otherwise let min2 be min - 1.
- If max = +∞, let max2 be +∞; otherwise let max2 be max - 1.
- Return
RepeatMatcher (m, min2, max2, greedy, y, c, parenIndex, parenCount).
- Let cap be a copy of x.[[Captures]].
- For each
integer k in theinclusive interval from parenIndex + 1 to parenIndex + parenCount, set cap[k] toundefined . - Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- Let xr be the
MatchState { [[Input]]: Input, [[EndIndex]]: e, [[Captures]]: cap }. - If min ≠ 0, return m(xr, d).
- If greedy is
false , then- Let z be c(x).
- If z is not
failure , return z. - Return m(xr, d).
- Let z be m(xr, d).
- If z is not
failure , return z. - Return c(x).
An
If the
Compare
/a[a-z]{2,4}/.exec("abcdefghi")which returns
/a[a-z]{2,4}?/.exec("abcdefghi")which returns
Consider also
/(aa|aabaac|ba|b|c)*/.exec("aabaac")which, by the choice point ordering above, returns the array
["aaba", "ba"]and not any of:
["aabaac", "aabaac"]
["aabaac", "c"]The above ordering of choice points can be used to write a regular expression that calculates the greatest common divisor of two numbers (represented in unary notation). The following example calculates the gcd of 10 and 15:
"aaaaaaaaaa,aaaaaaaaaaaaaaa".replace(/^(a+)\1*,\1+$/, "$1")which returns the gcd in unary notation
Step
/(z)((a+)?(b+)?(c))*/.exec("zaacbbbcac")which returns the array
["zaacbbbcac", "z", "ac", "a", undefined, "c"]and not
["zaacbbbcac", "z", "ac", "a", "bbb", "c"]because each iteration of the outermost * clears all captured Strings contained in
the
quantified
Step
/(a*)*/.exec("b")or the slightly more complicated:
/(a*)b\1+/.exec("baaaac")which returns the array
["b", ""]22.2.2.3.2 EmptyMatcher ( )
The abstract operation EmptyMatcher takes no arguments and returns a
- Return a new
Matcher with parameters (x, c) that captures nothing and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Return c(x).
22.2.2.3.3 MatchTwoAlternatives ( m1, m2 )
The abstract operation MatchTwoAlternatives takes arguments m1 (a
- Return a new
Matcher with parameters (x, c) that captures m1 and m2 and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let r be m1(x, c).
- If r is not
failure , return r. - Return m2(x, c).
22.2.2.3.4 MatchSequence ( m1, m2, direction )
The abstract operation MatchSequence takes arguments m1 (a
- If direction is
forward , then- Return a new
Matcher with parameters (x, c) that captures m1 and m2 and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures c and m2 and performs the following steps when called:Assert : y is aMatchState .- Return m2(y, c).
- Return m1(x, d).
- Return a new
- Else,
Assert : direction isbackward .- Return a new
Matcher with parameters (x, c) that captures m1 and m2 and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures c and m1 and performs the following steps when called:Assert : y is aMatchState .- Return m1(y, c).
- Return m2(x, d).
22.2.2.4 Runtime Semantics: CompileAssertion
The
This section is amended in
It is defined piecewise over the following productions:
- Return a new
Matcher with parameters (x, c) that captures rer and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- If e = 0, or if rer.[[Multiline]] is
true and the character Input[e - 1] is matched byLineTerminator , then- Return c(x).
- Return
failure .
Even when the y flag is used with a pattern, ^ always matches only at
the
beginning of Input, or (if rer.[[Multiline]] is
- Return a new
Matcher with parameters (x, c) that captures rer and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- Let InputLength be the number of elements in Input.
- If e = InputLength, or if
rer.[[Multiline]] is
true and the character Input[e] is matched byLineTerminator , then- Return c(x).
- Return
failure .
- Return a new
Matcher with parameters (x, c) that captures rer and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- Let a be
IsWordChar (rer, Input, e - 1). - Let b be
IsWordChar (rer, Input, e). - If a is
true and b isfalse , or if a isfalse and b istrue , return c(x). - Return
failure .
- Return a new
Matcher with parameters (x, c) that captures rer and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- Let a be
IsWordChar (rer, Input, e - 1). - Let b be
IsWordChar (rer, Input, e). - If a is
true and b istrue , or if a isfalse and b isfalse , return c(x). - Return
failure .
- Let m be
CompileSubpattern ofDisjunction with arguments rer andforward . - Return a new
Matcher with parameters (x, c) that captures m and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let r be m(x, d).
- If r is
failure , returnfailure . Assert : r is aMatchState .- Let cap be r.[[Captures]].
- Let Input be x.[[Input]].
- Let xe be x.[[EndIndex]].
- Let z be the
MatchState { [[Input]]: Input, [[EndIndex]]: xe, [[Captures]]: cap }. - Return c(z).
The form (?= )
specifies a zero-width positive lookahead. In order for it to succeed, the pattern inside (?= form (this unusual behaviour is
inherited
from Perl). This only matters when the
For example,
/(?=(a+))/.exec("baaabac")matches the empty String immediately after the first b and therefore returns the
array:
["", "aaa"]To illustrate the lack of backtracking into the lookahead, consider:
/(?=(a+))a*b\1/.exec("baaabac")This expression returns
["aba", "a"]and not:
["aaaba", "a"]- Let m be
CompileSubpattern ofDisjunction with arguments rer andforward . - Return a new
Matcher with parameters (x, c) that captures m and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let r be m(x, d).
- If r is not
failure , returnfailure . - Return c(x).
The form (?! )
specifies a zero-width negative lookahead. In order for it to succeed, the pattern inside
/(.*?)a(?!(a+)b\2c)\2(.*)/.exec("baaabaac")looks for an a not immediately followed by some positive number n of
a's,
a
b, another n a's (specified by the first \2) and a
c. The second \2 is outside the negative lookahead, so it matches
against
["baaabaac", "ba", undefined, "abaac"]- Let m be
CompileSubpattern ofDisjunction with arguments rer andbackward . - Return a new
Matcher with parameters (x, c) that captures m and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let r be m(x, d).
- If r is
failure , returnfailure . Assert : r is aMatchState .- Let cap be r.[[Captures]].
- Let Input be x.[[Input]].
- Let xe be x.[[EndIndex]].
- Let z be the
MatchState { [[Input]]: Input, [[EndIndex]]: xe, [[Captures]]: cap }. - Return c(z).
- Let m be
CompileSubpattern ofDisjunction with arguments rer andbackward . - Return a new
Matcher with parameters (x, c) that captures m and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let r be m(x, d).
- If r is not
failure , returnfailure . - Return c(x).
22.2.2.4.1 IsWordChar ( rer, Input, e )
The abstract operation IsWordChar takes arguments rer (a
- Let InputLength be the number of elements in Input.
- If e = -1 or e =
InputLength,
return
false . - Let c be the character Input[e].
- If
WordCharacters (rer) contains c, returntrue . - Return
false .
22.2.2.5 Runtime Semantics: CompileQuantifier
The
- Let qp be
CompileQuantifierPrefix ofQuantifierPrefix . - Return the
Record { [[Min]]: qp.[[Min]], [[Max]]: qp.[[Max]], [[Greedy]]:true }.
- Let qp be
CompileQuantifierPrefix ofQuantifierPrefix . - Return the
Record { [[Min]]: qp.[[Min]], [[Max]]: qp.[[Max]], [[Greedy]]:false }.
22.2.2.6 Runtime Semantics: CompileQuantifierPrefix
The
- Return the
Record { [[Min]]: 0, [[Max]]: +∞ }.
- Return the
Record { [[Min]]: 1, [[Max]]: +∞ }.
- Return the
Record { [[Min]]: 0, [[Max]]: 1 }.
- Let i be the MV of
DecimalDigits (see12.9.3 ). - Return the
Record { [[Min]]: i, [[Max]]: i }.
- Let i be the MV of
DecimalDigits . - Return the
Record { [[Min]]: i, [[Max]]: +∞ }.
- Let i be the MV of the first
DecimalDigits . - Let j be the MV of the second
DecimalDigits . - Return the
Record { [[Min]]: i, [[Max]]: j }.
22.2.2.7 Runtime Semantics: CompileAtom
The
This section is amended in
It is defined piecewise over the following productions:
- Let ch be the character matched by
PatternCharacter . - Let A be a one-element
CharSet containing the character ch. - Return
CharacterSetMatcher (rer, A,false , direction).
- Let A be
AllCharacters (rer). - If rer.[[DotAll]] is not
true , then- Remove from A all characters corresponding to
a
code point on the right-hand side of the
LineTerminator production.
- Remove from A all characters corresponding to
a
code point on the right-hand side of the
- Return
CharacterSetMatcher (rer, A,false , direction).
- Let cc be
CompileCharacterClass ofCharacterClass with argument rer. - Let cs be cc.[[CharSet]].
- If rer.[[UnicodeSets]] is
false , or if everyCharSetElement of cs consists of a single character (including if cs is empty), returnCharacterSetMatcher (rer, cs, cc.[[Invert]], direction). Assert : cc.[[Invert]] isfalse .- Let lm be an empty
List ofMatchers . - For each
CharSetElement s in cs containing more than 1 character, iterating in descending order of length, do- Let cs2 be a one-element
CharSet containing the last code point of s. - Let m2 be
CharacterSetMatcher (rer, cs2,false , direction). - For each code point c1 in s,
iterating
backwards from its second-to-last code point, do
- Let cs1 be a one-element
CharSet containing c1. - Let m1 be
CharacterSetMatcher (rer, cs1,false , direction). - Set m2 to
MatchSequence (m1, m2, direction).
- Let cs1 be a one-element
- Append m2 to lm.
- Let cs2 be a one-element
- Let singles be the
CharSet containing everyCharSetElement of cs that consists of a single character. - Append
CharacterSetMatcher (rer, singles,false , direction) to lm. - If cs contains the empty sequence of characters,
append
EmptyMatcher () to lm. - Let m2 be the last
Matcher in lm. - For each
Matcher m1 of lm, iterating backwards from its second-to-last element, do- Set m2 to
MatchTwoAlternatives (m1, m2).
- Set m2 to
- Return m2.
- Let m be
CompileSubpattern ofDisjunction with arguments rer and direction. - Let parenIndex be
CountLeftCapturingParensBefore (Atom ). - Return a new
Matcher with parameters (x, c) that captures direction, m, and parenIndex and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures x, c, direction, and parenIndex and performs the following steps when called:Assert : y is aMatchState .- Let cap be a copy of y.[[Captures]].
- Let Input be x.[[Input]].
- Let xe be x.[[EndIndex]].
- Let ye be y.[[EndIndex]].
- If direction is
forward , thenAssert : xe ≤ ye.- Let r be the
CaptureRange { [[StartIndex]]: xe, [[EndIndex]]: ye }.
- Else,
Assert : direction isbackward .Assert : ye ≤ xe.- Let r be the
CaptureRange { [[StartIndex]]: ye, [[EndIndex]]: xe }.
- Set cap[parenIndex + 1] to r.
- Let z be the
MatchState { [[Input]]: Input, [[EndIndex]]: ye, [[Captures]]: cap }. - Return c(z).
- Return m(x, d).
Parentheses of the form ( )
serve both to group the components of the \
followed by a non-zero decimal number), referenced in a replace String, or returned as part of an
array from the regular expression matching (?: ) instead.
- Return
CompileSubpattern ofDisjunction with arguments rer and direction.
- Let n be the
CapturingGroupNumber ofDecimalEscape . Assert : n ≤ rer.[[CapturingGroupsCount]].- Return
BackreferenceMatcher (rer, n, direction).
An escape sequence of the form \ followed by a non-zero decimal number n
matches the result of the nth set of capturing parentheses (
- Let cv be the
CharacterValue ofCharacterEscape . - Let ch be the character whose character value is cv.
- Let A be a one-element
CharSet containing the character ch. - Return
CharacterSetMatcher (rer, A,false , direction).
- Let cs be
CompileToCharSet ofCharacterClassEscape with argument rer. - If rer.[[UnicodeSets]] is
false , or if everyCharSetElement of cs consists of a single character (including if cs is empty), returnCharacterSetMatcher (rer, cs,false , direction). - Let lm be an empty
List ofMatchers . - For each
CharSetElement s in cs containing more than 1 character, iterating in descending order of length, do- Let cs2 be a one-element
CharSet containing the last code point of s. - Let m2 be
CharacterSetMatcher (rer, cs2,false , direction). - For each code point c1 in s,
iterating
backwards from its second-to-last code point, do
- Let cs1 be a one-element
CharSet containing c1. - Let m1 be
CharacterSetMatcher (rer, cs1,false , direction). - Set m2 to
MatchSequence (m1, m2, direction).
- Let cs1 be a one-element
- Append m2 to lm.
- Let cs2 be a one-element
- Let singles be the
CharSet containing everyCharSetElement of cs that consists of a single character. - Append
CharacterSetMatcher (rer, singles,false , direction) to lm. - If cs contains the empty sequence of characters,
append
EmptyMatcher () to lm. - Let m2 be the last
Matcher in lm. - For each
Matcher m1 of lm, iterating backwards from its second-to-last element, do- Set m2 to
MatchTwoAlternatives (m1, m2).
- Set m2 to
- Return m2.
- Let matchingGroupSpecifiers be
GroupSpecifiersThatMatch (GroupName ). Assert : matchingGroupSpecifiers contains a singleGroupSpecifier .- Let groupSpecifier be the sole element of matchingGroupSpecifiers.
- Let parenIndex be
CountLeftCapturingParensBefore (groupSpecifier). - Return
BackreferenceMatcher (rer, parenIndex, direction).
22.2.2.7.1 CharacterSetMatcher ( rer, A, invert, direction )
The abstract operation CharacterSetMatcher takes arguments rer (a
- If rer.[[UnicodeSets]]
is
true , thenAssert : invert isfalse .Assert : EveryCharSetElement of A consists of a single character.
- Return a new
Matcher with parameters (x, c) that captures rer, A, invert, and direction and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- If direction is
forward , let f be e + 1. - Else, let f be e - 1.
- Let InputLength be the number of elements in Input.
- If f < 0 or f >
InputLength, return
failure . - Let index be
min (e, f). - Let ch be the character Input[index].
- Let cc be
Canonicalize (rer, ch). - If there exists a
CharSetElement in A containing exactly one character a such thatCanonicalize (rer, a) is cc, let found betrue . Otherwise, let found befalse . - If invert is
false and found isfalse , returnfailure . - If invert is
true and found istrue , returnfailure . - Let cap be x.[[Captures]].
- Let y be the
MatchState { [[Input]]: Input, [[EndIndex]]: f, [[Captures]]: cap }. - Return c(y).
22.2.2.7.2 BackreferenceMatcher ( rer, n, direction )
The abstract operation BackreferenceMatcher takes arguments rer (a
Assert : n ≥ 1.- Return a new
Matcher with parameters (x, c) that captures rer, n, and direction and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let cap be x.[[Captures]].
- Let r be cap[n].
- If r is
undefined , return c(x). - Let e be x.[[EndIndex]].
- Let rs be r.[[StartIndex]].
- Let re be r.[[EndIndex]].
- Let len be re - rs.
- If direction is
forward , let f be e + len. - Else, let f be e - len.
- Let InputLength be the number of elements in Input.
- If f < 0 or f >
InputLength, return
failure . - Let g be
min (e, f). - If there exists an
integer i in theinterval from 0 (inclusive) to len (exclusive) such thatCanonicalize (rer, Input[rs + i]) is notCanonicalize (rer, Input[g + i]), returnfailure . - Let y be the
MatchState { [[Input]]: Input, [[EndIndex]]: f, [[Captures]]: cap }. - Return c(y).
22.2.2.7.3 Canonicalize ( rer, ch )
The abstract operation Canonicalize takes arguments rer (a
- If
HasEitherUnicodeFlag (rer) istrue and rer.[[IgnoreCase]] istrue , then- If the file
CaseFolding.txtof the Unicode Character Database provides a simple or common case folding mapping for ch, return the result of applying that mapping to ch. - Return ch.
- If the file
- If rer.[[IgnoreCase]]
is
false , return ch. Assert : ch is a UTF-16 code unit.- Let cp be the code point whose numeric value is the numeric value of ch.
- Let u be the result of toUppercase(« cp »), according to the Unicode Default Case Conversion algorithm.
- Let uStr be
CodePointsToString (u). - If the length of uStr ≠ 1, return ch.
- Let cu be uStr's single code unit element.
- If the numeric value of ch ≥ 128 and the numeric value of cu < 128, return ch.
- Return cu.
In case-insignificant matches when ß (U+00DF LATIN SMALL
LETTER SHARP S) to ss or SS. It may however map code points outside
the
Basic Latin block to code points within it—for example, ſ (U+017F LATIN SMALL
LETTER
LONG S) case-folds to s (U+0073 LATIN SMALL LETTER S) and K (U+212A
KELVIN
SIGN) case-folds to k (U+006B LATIN SMALL LETTER K). Strings containing those code
points are matched by regular expressions such as /[a-z]/ui.
In case-insignificant matches when Ω (U+2126 OHM SIGN) is mapped by toUppercase to itself but by toCasefold to
ω (U+03C9 GREEK SMALL LETTER OMEGA) along with Ω (U+03A9 GREEK CAPITAL
LETTER OMEGA), so /[ω]/ui and
/[\u03A9]/ui but not by /[ω]/i or /[\u03A9]/i. Also, no
code
point outside the Basic Latin block is mapped to a code point within it, so strings such as
/[a-z]/i.
22.2.2.8 Runtime Semantics: CompileCharacterClass
The
- Let A be
CompileToCharSet ofClassContents with argument rer. - Return the
Record { [[CharSet]]: A, [[Invert]]:false }.
- Let A be
CompileToCharSet ofClassContents with argument rer. - If rer.[[UnicodeSets]] is
true , then- Return the
Record { [[CharSet]]:CharacterComplement (rer, A), [[Invert]]:false }.
- Return the
- Return the
Record { [[CharSet]]: A, [[Invert]]:true }.
22.2.2.9 Runtime Semantics: CompileToCharSet
The
This section is amended in
It is defined piecewise over the following productions:
- Return the empty
CharSet .
- Let A be
CompileToCharSet ofClassAtom with argument rer. - Let B be
CompileToCharSet ofNonemptyClassRangesNoDash with argument rer. - Return the union of
CharSets A and B.
- Let A be
CompileToCharSet of the firstClassAtom with argument rer. - Let B be
CompileToCharSet of the secondClassAtom with argument rer. - Let C be
CompileToCharSet ofClassContents with argument rer. - Let D be
CharacterRange (A, B). - Return the union of D and C.
- Let A be
CompileToCharSet ofClassAtomNoDash with argument rer. - Let B be
CompileToCharSet ofNonemptyClassRangesNoDash with argument rer. - Return the union of
CharSets A and B.
- Let A be
CompileToCharSet ofClassAtomNoDash with argument rer. - Let B be
CompileToCharSet ofClassAtom with argument rer. - Let C be
CompileToCharSet ofClassContents with argument rer. - Let D be
CharacterRange (A, B). - Return the union of D and C.
Even if the pattern ignores case, the case of the two ends of a range is significant in
determining
which characters belong to the range. Thus, for example, the pattern /[E-F]/i matches
only the letters E, F, e, and f, while the
pattern
/[E-f]/i matches all uppercase and lowercase letters in the Unicode Basic Latin block
as
well as the symbols [, \, ], ^,
_,
and `.
A - character can be treated literally or it can denote a range. It is treated
literally
if it is the first or last character of
- Return the
CharSet containing the single character-U+002D (HYPHEN-MINUS).
- Return the
CharSet containing the character matched bySourceCharacter .
- Let cv be the
CharacterValue of thisClassEscape . - Let c be the character whose character value is cv.
- Return the
CharSet containing the single character c.
A \b,
\B, and backreferences. Inside a \b means the backspace character, while \B and backreferences raise
errors.
Using a backreference inside a
- Return the ten-element
CharSet containing the characters0,1,2,3,4,5,6,7,8, and9.
- Let S be the
CharSet returned byCharacterClassEscape :: d - Return
CharacterComplement (rer, S).
- Return the
CharSet containing all characters corresponding to a code point on the right-hand side of theWhiteSpace orLineTerminator productions.
- Let S be the
CharSet returned byCharacterClassEscape :: s - Return
CharacterComplement (rer, S).
- Return
MaybeSimpleCaseFolding (rer,WordCharacters (rer)).
- Let S be the
CharSet returned byCharacterClassEscape :: w - Return
CharacterComplement (rer, S).
- Return
CompileToCharSet ofUnicodePropertyValueExpression with argument rer.
- Let S be
CompileToCharSet ofUnicodePropertyValueExpression with argument rer. Assert : S contains only single code points.- Return
CharacterComplement (rer, S).
- Let ps be the
source text matched by UnicodePropertyName . - Let p be
UnicodeMatchProperty (rer, ps). Assert : p is a Unicodeproperty name or property alias listed in the “Property name and aliases” column ofTable 67 .- Let vs be the
source text matched by UnicodePropertyValue . - Let v be
UnicodeMatchPropertyValue (p, vs). - Let A be the
CharSet containing all Unicode code points whose character database definition includes the property p with value v. - Return
MaybeSimpleCaseFolding (rer, A).
- Let s be the
source text matched by LoneUnicodePropertyNameOrValue . - If
UnicodeMatchPropertyValue (General_Category, s) is a Unicode property value or property value alias for the General_Category (gc) property listed inPropertyValueAliases.txt, then- Return the
CharSet containing all Unicode code points whose character database definition includes the property “General_Category” with value s.
- Return the
- Let p be
UnicodeMatchProperty (rer, s). Assert : p is a binary Unicode property or binary property alias listed in the “Property name and aliases” column ofTable 68 , or a binary Unicode property of strings listed in the “Property name ” column ofTable 69 .- Let A be the
CharSet containing all CharSetElements whose character database definition includes the property p with value “True”. - Return
MaybeSimpleCaseFolding (rer, A).
- Let A be
CompileToCharSet ofClassSetRange with argument rer. - If
ClassUnion is present, then- Let B be
CompileToCharSet ofClassUnion with argument rer. - Return the union of
CharSets A and B.
- Let B be
- Return A.
- Let A be
CompileToCharSet ofClassSetOperand with argument rer. - If
ClassUnion is present, then- Let B be
CompileToCharSet ofClassUnion with argument rer. - Return the union of
CharSets A and B.
- Let B be
- Return A.
- Let A be
CompileToCharSet of the firstClassSetOperand with argument rer. - Let B be
CompileToCharSet of the secondClassSetOperand with argument rer. - Return the intersection of
CharSets A and B.
- Let A be
CompileToCharSet of theClassIntersection with argument rer. - Let B be
CompileToCharSet of theClassSetOperand with argument rer. - Return the intersection of
CharSets A and B.
- Let A be
CompileToCharSet of the firstClassSetOperand with argument rer. - Let B be
CompileToCharSet of the secondClassSetOperand with argument rer. - Return the
CharSet containing the CharSetElements of A which are not also CharSetElements of B.
- Let A be
CompileToCharSet of theClassSubtraction with argument rer. - Let B be
CompileToCharSet of theClassSetOperand with argument rer. - Return the
CharSet containing the CharSetElements of A which are not also CharSetElements of B.
- Let A be
CompileToCharSet of the firstClassSetCharacter with argument rer. - Let B be
CompileToCharSet of the secondClassSetCharacter with argument rer. - Return
MaybeSimpleCaseFolding (rer,CharacterRange (A, B)).
The result will often consist of two or more ranges. When UnicodeSets is
- Let A be
CompileToCharSet ofClassSetCharacter with argument rer. - Return
MaybeSimpleCaseFolding (rer, A).
- Let A be
CompileToCharSet ofClassStringDisjunction with argument rer. - Return
MaybeSimpleCaseFolding (rer, A).
- Return
CompileToCharSet ofNestedClass with argument rer.
- Return
CompileToCharSet ofClassContents with argument rer.
- Let A be
CompileToCharSet ofClassContents with argument rer. - Return
CharacterComplement (rer, A).
- Return
CompileToCharSet ofCharacterClassEscape with argument rer.
- Return
CompileToCharSet ofClassStringDisjunctionContents with argument rer.
- Let s be
CompileClassSetString ofClassString with argument rer. - Return the
CharSet containing the one string s.
- Let s be
CompileClassSetString ofClassString with argument rer. - Let A be the
CharSet containing the one string s. - Let B be
CompileToCharSet ofClassStringDisjunctionContents with argument rer. - Return the union of
CharSets A and B.
- Let cv be the
CharacterValue of thisClassSetCharacter . - Let c be the character whose character value is cv.
- Return the
CharSet containing the single character c.
- Return the
CharSet containing the single character U+0008 (BACKSPACE).
22.2.2.9.1 CharacterRange ( A, B )
The abstract operation CharacterRange takes arguments A (a
Assert : A and B each contain exactly one character.- Let a be the one character in
CharSet A. - Let b be the one character in
CharSet B. - Let i be the character value of character a.
- Let j be the character value of character b.
Assert : i ≤ j.- Return the
CharSet containing all characters with a character value in theinclusive interval from i to j.
22.2.2.9.2 HasEitherUnicodeFlag ( rer )
The abstract operation HasEitherUnicodeFlag takes argument rer (a
- If rer.[[Unicode]] is
true or rer.[[UnicodeSets]] istrue , then- Return
true .
- Return
- Return
false .
22.2.2.9.3 WordCharacters ( rer )
The abstract operation WordCharacters takes argument rer (a \b, \B,
\w, and \W It performs the following steps when called:
- Let basicWordChars be the
CharSet containing every character inthe ASCII word characters . - Let extraWordChars be the
CharSet containing all characters c such that c is not in basicWordChars butCanonicalize (rer, c) is in basicWordChars. Assert : extraWordChars is empty unlessHasEitherUnicodeFlag (rer) istrue and rer.[[IgnoreCase]] istrue .- Return the union of basicWordChars and extraWordChars.
22.2.2.9.4 AllCharacters ( rer )
The abstract operation AllCharacters takes argument rer (a
- If rer.[[UnicodeSets]]
is
true and rer.[[IgnoreCase]] istrue , then- Return the
CharSet containing all Unicode code points c that do not have a Simple Case Folding mapping (that is,scf (c)=c).
- Return the
- Else if
HasEitherUnicodeFlag (rer) istrue , then- Return the
CharSet containing all code point values.
- Return the
- Else,
- Return the
CharSet containing all code unit values.
- Return the
22.2.2.9.5 MaybeSimpleCaseFolding ( rer, A )
The abstract operation MaybeSimpleCaseFolding takes arguments rer (a CaseFolding.txt
of
the Unicode Character Database (each of which maps a single code point to another single code point)
to
map each
- If rer.[[UnicodeSets]]
is
false or rer.[[IgnoreCase]] isfalse , return A. - Let B be a new empty
CharSet . - For each
CharSetElement s of A, do- Let t be an empty sequence of characters.
- For each single code point cp in
s,
do
- Append
scf (cp) to t.
- Append
- Add t to B.
- Return B.
22.2.2.9.6 CharacterComplement ( rer, S )
The abstract operation CharacterComplement takes arguments rer (a
- Let A be
AllCharacters (rer). - Return the
CharSet containing the CharSetElements of A which are not also CharSetElements of S.
22.2.2.9.7 UnicodeMatchProperty ( rer, p )
The abstract operation UnicodeMatchProperty takes arguments rer (a
- If rer.[[UnicodeSets]]
is
true and p is a Unicodeproperty name listed in the “Property name ” column ofTable 69 , then- Return the
List of Unicode code points p.
- Return the
Assert : p is a Unicodeproperty name or property alias listed in the “Property name and aliases” column ofTable 67 orTable 68 .- Let c be the canonical
property name of p as given in the “Canonicalproperty name ” column of the corresponding row. - Return the
List of Unicode code points c.
Implementations must support the Unicode property names and aliases listed in
For example, Script_Extensions (scx (property alias) are valid, but script_extensions or
Scx
aren't.
The listed properties form a superset of what UTS18 RL1.2 requires.
The spellings of entries in these tables (including casing) match the spellings used in the
file
PropertyAliases.txt
in the Unicode Character Database. The precise spellings in that file are guaranteed to be
stable.
| Canonical |
|
|---|---|
General_Category |
General_Category
|
gc |
|
Script |
Script
|
sc |
|
Script_Extensions |
Script_Extensions
|
scx |
| Canonical |
|
|---|---|
ASCII |
ASCII
|
ASCII_Hex_Digit |
ASCII_Hex_Digit
|
AHex |
|
Alphabetic |
Alphabetic |
Alpha |
|
Any |
Any
|
Assigned |
Assigned
|
Bidi_Control |
Bidi_Control
|
Bidi_C |
|
Bidi_Mirrored |
Bidi_Mirrored
|
Bidi_M |
|
Case_Ignorable |
Case_Ignorable
|
CI |
|
Cased |
Cased |
Changes_When_Casefolded |
Changes_When_Casefolded
|
CWCF |
|
Changes_When_Casemapped |
Changes_When_Casemapped
|
CWCM |
|
Changes_When_Lowercased |
Changes_When_Lowercased
|
CWL |
|
Changes_When_NFKC_Casefolded |
Changes_When_NFKC_Casefolded
|
CWKCF |
|
Changes_When_Titlecased |
Changes_When_Titlecased
|
CWT |
|
Changes_When_Uppercased |
Changes_When_Uppercased
|
CWU |
|
Dash |
Dash |
Default_Ignorable_Code_Point |
Default_Ignorable_Code_Point
|
DI |
|
Deprecated |
Deprecated |
Dep |
|
Diacritic |
Diacritic |
Dia |
|
Emoji |
Emoji
|
Emoji_Component |
Emoji_Component
|
EComp |
|
Emoji_Modifier |
Emoji_Modifier
|
EMod |
|
Emoji_Modifier_Base |
Emoji_Modifier_Base
|
EBase |
|
Emoji_Presentation |
Emoji_Presentation
|
EPres |
|
Extended_Pictographic |
Extended_Pictographic
|
ExtPict |
|
Extender |
Extender
|
Ext |
|
Grapheme_Base |
Grapheme_Base
|
Gr_Base |
|
Grapheme_Extend |
Grapheme_Extend
|
Gr_Ext |
|
Hex_Digit |
Hex_Digit |
Hex |
|
IDS_Binary_Operator |
IDS_Binary_Operator
|
IDSB |
|
IDS_Trinary_Operator |
IDS_Trinary_Operator
|
IDST |
|
ID_Continue |
ID_Continue |
IDC |
|
ID_Start |
ID_Start
|
IDS |
|
Ideographic |
Ideographic |
Ideo |
|
Join_Control |
Join_Control
|
Join_C |
|
Logical_Order_Exception |
Logical_Order_Exception
|
LOE |
|
Lowercase |
Lowercase |
Lower |
|
Math |
Math |
Noncharacter_Code_Point |
Noncharacter_Code_Point
|
NChar |
|
Pattern_Syntax |
Pattern_Syntax
|
Pat_Syn |
|
Pattern_White_Space |
Pattern_White_Space
|
Pat_WS |
|
Quotation_Mark |
Quotation_Mark
|
QMark |
|
Radical |
Radical |
Regional_Indicator |
Regional_Indicator
|
RI |
|
Sentence_Terminal |
Sentence_Terminal |
STerm |
|
Soft_Dotted |
Soft_Dotted |
SD |
|
Terminal_Punctuation |
Terminal_Punctuation
|
Term |
|
Unified_Ideograph |
Unified_Ideograph
|
UIdeo |
|
Uppercase |
Uppercase |
Upper |
|
Variation_Selector |
Variation_Selector
|
VS |
|
White_Space |
White_Space |
space |
|
XID_Continue |
XID_Continue
|
XIDC |
|
XID_Start |
XID_Start |
XIDS |
Basic_Emoji |
Emoji_Keycap_Sequence |
RGI_Emoji_Modifier_Sequence |
RGI_Emoji_Flag_Sequence |
RGI_Emoji_Tag_Sequence |
RGI_Emoji_ZWJ_Sequence |
RGI_Emoji |
22.2.2.9.8 UnicodeMatchPropertyValue ( p, v )
The abstract operation UnicodeMatchPropertyValue takes arguments p (
Assert : p is a canonical, unaliased Unicodeproperty name listed in the “Canonicalproperty name ” column ofTable 67 .Assert : v is a property value or property value alias for the Unicode property p listed inPropertyValueAliases.txt.- Let value be the canonical property value of v as given in the “Canonical property value” column of the corresponding row.
- Return the
List of Unicode code points value.
Implementations must support the Unicode property values and property value aliases listed in PropertyValueAliases.txt
for the properties listed in
For example, Xpeo and Old_Persian are valid
Script_Extensions values, but xpeo and Old Persian
aren't.
This algorithm differs from the
matching rules for symbolic values listed in UAX44: case, Is prefix is
not
supported.
22.2.2.10 Runtime Semantics: CompileClassSetString
The
- Return an empty sequence of characters.
- Return
CompileClassSetString ofNonEmptyClassString with argument rer.
- Let cs be
CompileToCharSet ofClassSetCharacter with argument rer. - Let s1 be the sequence of characters that is the
single
CharSetElement of cs. - If
NonEmptyClassString is present, then- Let s2 be
CompileClassSetString ofNonEmptyClassString with argument rer. - Return the concatenation of s1 and s2.
- Let s2 be
- Return s1.
22.2.3 Abstract Operations for RegExp Creation
22.2.3.1 RegExpCreate ( P, F )
The abstract operation RegExpCreate takes arguments P (an
- Let obj be !
RegExpAlloc (%RegExp% ). - Return ?
RegExpInitialize (obj, P, F).
22.2.3.2 RegExpAlloc ( newTarget )
The abstract operation RegExpAlloc takes argument newTarget (a
- Let obj be ?
OrdinaryCreateFromConstructor (newTarget,"%RegExp.prototype%" , « [[OriginalSource]], [[OriginalFlags]], [[RegExpRecord]], [[RegExpMatcher]] »). - Perform !
DefinePropertyOrThrow (obj,"lastIndex" , PropertyDescriptor { [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return obj.
22.2.3.3 RegExpInitialize ( obj, pattern, flags )
The abstract operation RegExpInitialize takes arguments obj (an Object),
pattern
(an
- If pattern is
undefined , let P be the empty String. - Else, let P be ?
ToString (pattern). - If flags is
undefined , let F be the empty String. - Else, let F be ?
ToString (flags). - If F contains any code unit other than
"d" ,"g" ,"i" ,"m" ,"s" ,"u" ,"v" , or"y" , or if F contains any code unit more than once, throw aSyntaxError exception. - If F contains
"i" , let i betrue ; else let i befalse . - If F contains
"m" , let m betrue ; else let m befalse . - If F contains
"s" , let s betrue ; else let s befalse . - If F contains
"u" , let u betrue ; else let u befalse . - If F contains
"v" , let v betrue ; else let v befalse . - If u is
true or v istrue , then- Let patternText be
StringToCodePoints (P).
- Let patternText be
- Else,
- Let patternText be the result of interpreting each of P's 16-bit elements as a Unicode BMP code point. UTF-16 decoding is not applied to the elements.
- Let parseResult be
ParsePattern (patternText, u, v). - If parseResult is a non-empty
List ofSyntaxError objects, throw aSyntaxError exception. Assert : parseResult is aPattern Parse Node .- Set obj.[[OriginalSource]] to P.
- Set obj.[[OriginalFlags]] to F.
- Let capturingGroupsCount be
CountLeftCapturingParensWithin (parseResult). - Let rer be the
RegExp Record { [[IgnoreCase]]: i, [[Multiline]]: m, [[DotAll]]: s, [[Unicode]]: u, [[UnicodeSets]]: v, [[CapturingGroupsCount]]: capturingGroupsCount }. - Set obj.[[RegExpRecord]] to rer.
- Set obj.[[RegExpMatcher]]
to
CompilePattern of parseResult with argument rer. - Perform ?
Set (obj,"lastIndex" ,+0 𝔽,true ). - Return obj.
22.2.3.4 Static Semantics: ParsePattern ( patternText, u, v )
The abstract operation ParsePattern takes arguments patternText (a sequence of Unicode
code
points), u (a Boolean), and v (a Boolean) and returns a
This section is amended in
It performs the following steps when called:
- If v is
true and u istrue , then- Let parseResult be a
List containing one or moreSyntaxError objects.
- Let parseResult be a
- Else if v is
true , then - Else if u is
true , then - Else,
- Return parseResult.
22.2.4 The RegExp Constructor
The RegExp
- is %RegExp%.
- is the initial value of the
"RegExp" property of theglobal object . - creates and initializes a new RegExp object when called as a
constructor . - when called as a function rather than as a
constructor , returns either a new RegExp object, or the argument itself if the only argument is a RegExp object. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified RegExp behaviour must include asupercall to the RegExpconstructor to create and initialize subclass instances with the necessary internal slots.
22.2.4.1 RegExp ( pattern, flags )
This function performs the following steps when called:
- Let patternIsRegExp be ?
IsRegExp (pattern). - If NewTarget is
undefined , then- Let newTarget be the
active function object . - If patternIsRegExp is
true and flags isundefined , then
- Let newTarget be the
- Else,
- Let newTarget be NewTarget.
- If pattern
is an Object and pattern has a [[RegExpMatcher]] internal slot, then- Let P be pattern.[[OriginalSource]].
- If flags is
undefined , let F be pattern.[[OriginalFlags]]. - Else, let F be flags.
- Else if patternIsRegExp is
true , then - Else,
- Let P be pattern.
- Let F be flags.
- Let O be ?
RegExpAlloc (newTarget). - Return ?
RegExpInitialize (O, P, F).
If pattern is supplied using a
22.2.5 Properties of the RegExp Constructor
The RegExp
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
22.2.5.1 RegExp.prototype
The initial value of RegExp.prototype is the
This property has the attributes { [[Writable]]:
22.2.5.2 get RegExp [ @@species ]
RegExp[@@species] is an
- Return the
this value.
The value of the
RegExp prototype methods normally use their
22.2.6 Properties of the RegExp Prototype Object
The RegExp prototype object:
- is %RegExp.prototype%.
- is an
ordinary object . - is not a RegExp instance and does not have a [[RegExpMatcher]] internal slot or any of the other internal slots of RegExp instance objects.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
The RegExp prototype object does not have a
22.2.6.1 RegExp.prototype.constructor
The initial value of RegExp.prototype.constructor is
22.2.6.2 RegExp.prototype.exec ( string )
This method searches string for an occurrence of the regular expression pattern and
returns
an
Array containing the results of the match, or
It performs the following steps when called:
- Let R be the
this value. - Perform ?
RequireInternalSlot (R, [[RegExpMatcher]]). - Let S be ?
ToString (string). - Return ?
RegExpBuiltinExec (R, S).
22.2.6.3 get RegExp.prototype.dotAll
RegExp.prototype.dotAll is an
- Let R be the
this value. - Let cu be the code unit 0x0073 (LATIN SMALL LETTER S).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.4 get RegExp.prototype.flags
RegExp.prototype.flags is an
- Let R be the
this value. - If R
is not an Object , throw aTypeError exception. - Let codeUnits be a new empty
List . - Let hasIndices be
ToBoolean (?Get (R,"hasIndices" )). - If hasIndices is
true , append the code unit 0x0064 (LATIN SMALL LETTER D) to codeUnits. - Let global be
ToBoolean (?Get (R,"global" )). - If global is
true , append the code unit 0x0067 (LATIN SMALL LETTER G) to codeUnits. - Let ignoreCase be
ToBoolean (?Get (R,"ignoreCase" )). - If ignoreCase is
true , append the code unit 0x0069 (LATIN SMALL LETTER I) to codeUnits. - Let multiline be
ToBoolean (?Get (R,"multiline" )). - If multiline is
true , append the code unit 0x006D (LATIN SMALL LETTER M) to codeUnits. - Let dotAll be
ToBoolean (?Get (R,"dotAll" )). - If dotAll is
true , append the code unit 0x0073 (LATIN SMALL LETTER S) to codeUnits. - Let unicode be
ToBoolean (?Get (R,"unicode" )). - If unicode is
true , append the code unit 0x0075 (LATIN SMALL LETTER U) to codeUnits. - Let unicodeSets be
ToBoolean (?Get (R,"unicodeSets" )). - If unicodeSets is
true , append the code unit 0x0076 (LATIN SMALL LETTER V) to codeUnits. - Let sticky be
ToBoolean (?Get (R,"sticky" )). - If sticky is
true , append the code unit 0x0079 (LATIN SMALL LETTER Y) to codeUnits. - Return the String value whose code units are the elements of
the
List codeUnits. If codeUnits has no elements, the empty String is returned.
22.2.6.4.1 RegExpHasFlag ( R, codeUnit )
The abstract operation RegExpHasFlag takes arguments R (an
- If R
is not an Object , throw aTypeError exception. - If R does not have an [[OriginalFlags]] internal slot, then
- If
SameValue (R,%RegExp.prototype% ) istrue , returnundefined . - Otherwise, throw a
TypeError exception.
- If
- Let flags be R.[[OriginalFlags]].
- If flags contains codeUnit, return
true . - Return
false .
22.2.6.5 get RegExp.prototype.global
RegExp.prototype.global is an
- Let R be the
this value. - Let cu be the code unit 0x0067 (LATIN SMALL LETTER G).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.6 get RegExp.prototype.hasIndices
RegExp.prototype.hasIndices is an
- Let R be the
this value. - Let cu be the code unit 0x0064 (LATIN SMALL LETTER D).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.7 get RegExp.prototype.ignoreCase
RegExp.prototype.ignoreCase is an
- Let R be the
this value. - Let cu be the code unit 0x0069 (LATIN SMALL LETTER I).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.8 RegExp.prototype [ @@match ] ( string )
This method performs the following steps when called:
- Let rx be the
this value. - If rx
is not an Object , throw aTypeError exception. - Let S be ?
ToString (string). - Let flags be ?
ToString (?Get (rx,"flags" )). - If flags does not contain
"g" , then- Return ?
RegExpExec (rx, S).
- Return ?
- Else,
- If flags contains
"u" or flags contains"v" , let fullUnicode betrue . Otherwise, let fullUnicode befalse . - Perform ?
Set (rx,"lastIndex" ,+0 𝔽,true ). - Let A be !
ArrayCreate (0). - Let n be 0.
- Repeat,
- Let result be ?
RegExpExec (rx, S). - If result is
null , then- If n = 0, return
null . - Return A.
- If n = 0, return
- Else,
- Let matchStr be ?
ToString (?Get (result,"0" )). - Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), matchStr). - If matchStr is the empty String, then
- Set n to n + 1.
- Let matchStr be ?
- Let result be ?
- If flags contains
The value of the
The
22.2.6.9 RegExp.prototype [ @@matchAll ] ( string )
This method performs the following steps when called:
- Let R be the
this value. - If R
is not an Object , throw aTypeError exception. - Let S be ?
ToString (string). - Let C be ?
SpeciesConstructor (R,%RegExp% ). - Let flags be ?
ToString (?Get (R,"flags" )). - Let matcher be ?
Construct (C, « R, flags »). - Let lastIndex be ?
ToLength (?Get (R,"lastIndex" )). - Perform ?
Set (matcher,"lastIndex" , lastIndex,true ). - If flags contains
"g" , let global betrue . - Else, let global be
false . - If flags contains
"u" or flags contains"v" , let fullUnicode betrue . - Else, let fullUnicode be
false . - Return
CreateRegExpStringIterator (matcher, S, global, fullUnicode).
The value of the
22.2.6.10 get RegExp.prototype.multiline
RegExp.prototype.multiline is an
- Let R be the
this value. - Let cu be the code unit 0x006D (LATIN SMALL LETTER M).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.11 RegExp.prototype [ @@replace ] ( string, replaceValue )
This method performs the following steps when called:
- Let rx be the
this value. - If rx
is not an Object , throw aTypeError exception. - Let S be ?
ToString (string). - Let lengthS be the length of S.
- Let functionalReplace be
IsCallable (replaceValue). - If functionalReplace is
false , then- Set replaceValue to ?
ToString (replaceValue).
- Set replaceValue to ?
- Let flags be ?
ToString (?Get (rx,"flags" )). - If flags contains
"g" , let global betrue . Otherwise, let global befalse . - If global is
true , then- Perform ?
Set (rx,"lastIndex" ,+0 𝔽,true ).
- Perform ?
- Let results be a new empty
List . - Let done be
false . - Repeat, while done is
false ,- Let result be ?
RegExpExec (rx, S). - If result is
null , then- Set done to
true .
- Set done to
- Else,
- Let result be ?
- Let accumulatedResult be the empty String.
- Let nextSourcePosition be 0.
- For each element result of results, do
- Let resultLength be ?
LengthOfArrayLike (result). - Let nCaptures be
max (resultLength - 1, 0). - Let matched be ?
ToString (?Get (result,"0" )). - Let matchLength be the length of matched.
- Let position be ?
ToIntegerOrInfinity (?Get (result,"index" )). - Set position to the result of
clamping position between 0 and lengthS. - Let captures be a new empty
List . - Let n be 1.
- Repeat, while n ≤ nCaptures,
- Let capN be ?
Get (result, !ToString (𝔽 (n))). - If capN is not
undefined , then- Set capN to ?
ToString (capN).
- Set capN to ?
- Append capN to captures.
- NOTE: When n = 1, the preceding step puts the first element into captures (at index 0). More generally, the nth capture (the characters captured by the nth set of capturing parentheses) is at captures[n - 1].
- Set n to n + 1.
- Let capN be ?
- Let namedCaptures be ?
Get (result,"groups" ). - If functionalReplace is
true , then- Let replacerArgs be the
list-concatenation of « matched », captures, and «𝔽 (position), S ». - If namedCaptures is not
undefined , then- Append namedCaptures to replacerArgs.
- Let replValue be ?
Call (replaceValue,undefined , replacerArgs). - Let replacement be ?
ToString (replValue).
- Let replacerArgs be the
- Else,
- If namedCaptures is not
undefined , then- Set namedCaptures to ?
ToObject (namedCaptures).
- Set namedCaptures to ?
- Let replacement be ?
GetSubstitution (matched, S, position, captures, namedCaptures, replaceValue).
- If namedCaptures is not
- If position ≥ nextSourcePosition,
then
- NOTE: position should not normally move backwards. If it does, it is an indication of an ill-behaving RegExp subclass or use of an access triggered side-effect to change the global flag or other characteristics of rx. In such cases, the corresponding substitution is ignored.
- Set accumulatedResult to the
string-concatenation of accumulatedResult, thesubstring of S from nextSourcePosition to position, and replacement. - Set nextSourcePosition to position + matchLength.
- Let resultLength be ?
- If nextSourcePosition ≥ lengthS, return accumulatedResult.
- Return the
string-concatenation of accumulatedResult and thesubstring of S from nextSourcePosition.
The value of the
22.2.6.12 RegExp.prototype [ @@search ] ( string )
This method performs the following steps when called:
- Let rx be the
this value. - If rx
is not an Object , throw aTypeError exception. - Let S be ?
ToString (string). - Let previousLastIndex be ?
Get (rx,"lastIndex" ). - If
SameValue (previousLastIndex,+0 𝔽) isfalse , then- Perform ?
Set (rx,"lastIndex" ,+0 𝔽,true ).
- Perform ?
- Let result be ?
RegExpExec (rx, S). - Let currentLastIndex be ?
Get (rx,"lastIndex" ). - If
SameValue (currentLastIndex, previousLastIndex) isfalse , then- Perform ?
Set (rx,"lastIndex" , previousLastIndex,true ).
- Perform ?
- If result is
null , return-1 𝔽. - Return ?
Get (result,"index" ).
The value of the
The
22.2.6.13 get RegExp.prototype.source
RegExp.prototype.source is an
- Let R be the
this value. - If R
is not an Object , throw aTypeError exception. - If R does not have an [[OriginalSource]] internal slot, then
- If
SameValue (R,%RegExp.prototype% ) istrue , return"(?:)" . - Otherwise, throw a
TypeError exception.
- If
Assert : R has an [[OriginalFlags]] internal slot.- Let src be R.[[OriginalSource]].
- Let flags be R.[[OriginalFlags]].
- Return
EscapeRegExpPattern (src, flags).
22.2.6.13.1 EscapeRegExpPattern ( P, F )
The abstract operation EscapeRegExpPattern takes arguments P (a String) and F (a String) and returns a String. It performs the following steps when called:
- If F contains
"v" , then- Let patternSymbol be
Pattern .[+UnicodeMode, +UnicodeSetsMode]
- Let patternSymbol be
- Else if F contains
"u" , then- Let patternSymbol be
Pattern .[+UnicodeMode, ~UnicodeSetsMode]
- Let patternSymbol be
- Else,
- Let patternSymbol be
Pattern .[~UnicodeMode, ~UnicodeSetsMode]
- Let patternSymbol be
- Let S be a String in the form of a
patternSymbol equivalent to P interpreted as UTF-16 encoded Unicode code
points (
6.1.4 ), in which certain code points are escaped as described below. S may or may not differ from P; however, theAbstract Closure that would result from evaluating S as a patternSymbol must behave identically to theAbstract Closure given by the constructed object's [[RegExpMatcher]] internal slot. Multiple calls to this abstract operation using the same values for P and F must produce identical results. - The code points
/or anyLineTerminator occurring in the pattern shall be escaped in S as necessary to ensure that thestring-concatenation of"/" , S,"/" , and F can be parsed (in an appropriate lexical context) as aRegularExpressionLiteral that behaves identically to the constructed regular expression. For example, if P is"/" , then S could be"\/" or"\u002F" , among other possibilities, but not"/" , because///followed by F would be parsed as aSingleLineComment rather than aRegularExpressionLiteral . If P is the empty String, this specification can be met by letting S be"(?:)" . - Return S.
22.2.6.14 RegExp.prototype [ @@split ] ( string, limit )
This method returns an Array into which substrings of the result of converting string
to
a
String have been stored. The substrings are determined by searching from left to right for matches
of
the
The /a*?/[Symbol.split]("ab") evaluates to the array ["a", "b"], while
/a*/[Symbol.split]("ab") evaluates to the array ["","b"].)
If string is (or converts to) the empty String, the result depends on whether the regular expression can match the empty String. If it can, the result array contains no elements. Otherwise, the result array contains one element, which is the empty String.
If the regular expression contains capturing parentheses, then each time separator is
matched the results (including any
/<(\/)?([^<>]+)>/[Symbol.split]("A<B>bold</B>and<CODE>coded</CODE>")evaluates to the array
["A", undefined, "B", "bold", "/", "B", "and", undefined, "CODE", "coded", "/", "CODE", ""]If limit is not
This method performs the following steps when called:
- Let rx be the
this value. - If rx
is not an Object , throw aTypeError exception. - Let S be ?
ToString (string). - Let C be ?
SpeciesConstructor (rx,%RegExp% ). - Let flags be ?
ToString (?Get (rx,"flags" )). - If flags contains
"u" or flags contains"v" , let unicodeMatching betrue . - Else, let unicodeMatching be
false . - If flags contains
"y" , let newFlags be flags. - Else, let newFlags be the
string-concatenation of flags and"y" . - Let splitter be ?
Construct (C, « rx, newFlags »). - Let A be !
ArrayCreate (0). - Let lengthA be 0.
- If limit is
undefined , let lim be 232 - 1; else let lim beℝ (?ToUint32 (limit)). - If lim = 0, return A.
- If S is the empty String, then
- Let z be ?
RegExpExec (splitter, S). - If z is not
null , return A. - Perform !
CreateDataPropertyOrThrow (A,"0" , S). - Return A.
- Let z be ?
- Let size be the length of S.
- Let p be 0.
- Let q be p.
- Repeat, while q < size,
- Perform ?
Set (splitter,"lastIndex" ,𝔽 (q),true ). - Let z be ?
RegExpExec (splitter, S). - If z is
null , then- Set q to
AdvanceStringIndex (S, q, unicodeMatching).
- Set q to
- Else,
- Let e be
ℝ (?ToLength (?Get (splitter,"lastIndex" ))). - Set e to
min (e, size). - If e = p, then
- Set q to
AdvanceStringIndex (S, q, unicodeMatching).
- Set q to
- Else,
- Let T be the
substring of S from p to q. - Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (lengthA)), T). - Set lengthA to lengthA + 1.
- If lengthA = lim, return A.
- Set p to e.
- Let numberOfCaptures be
?
LengthOfArrayLike (z). - Set numberOfCaptures to
max (numberOfCaptures - 1, 0). - Let i be 1.
- Repeat, while i ≤ numberOfCaptures,
- Set q to p.
- Let T be the
- Let e be
- Perform ?
- Let T be the
substring of S from p to size. - Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (lengthA)), T). - Return A.
The value of the
This method ignores the value of the
22.2.6.15 get RegExp.prototype.sticky
RegExp.prototype.sticky is an
- Let R be the
this value. - Let cu be the code unit 0x0079 (LATIN SMALL LETTER Y).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.16 RegExp.prototype.test ( S )
This method performs the following steps when called:
- Let R be the
this value. - If R
is not an Object , throw aTypeError exception. - Let string be ?
ToString (S). - Let match be ?
RegExpExec (R, string). - If match is not
null , returntrue ; else returnfalse .
22.2.6.17 RegExp.prototype.toString ( )
- Let R be the
this value. - If R
is not an Object , throw aTypeError exception. - Let pattern be ?
ToString (?Get (R,"source" )). - Let flags be ?
ToString (?Get (R,"flags" )). - Let result be the
string-concatenation of"/" , pattern,"/" , and flags. - Return result.
The returned String has the form of a
22.2.6.18 get RegExp.prototype.unicode
RegExp.prototype.unicode is an
- Let R be the
this value. - Let cu be the code unit 0x0075 (LATIN SMALL LETTER U).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.19 get RegExp.prototype.unicodeSets
RegExp.prototype.unicodeSets is an
- Let R be the
this value. - Let cu be the code unit 0x0076 (LATIN SMALL LETTER V).
- Return ?
RegExpHasFlag (R, cu).
22.2.7 Abstract Operations for RegExp Matching
22.2.7.1 RegExpExec ( R, S )
The abstract operation RegExpExec takes arguments R (an Object) and S (a
String)
and returns either a
- Let exec be ?
Get (R,"exec" ). - If
IsCallable (exec) istrue , then- Let result be ?
Call (exec, R, « S »). - If result
is not an Object and result is notnull , throw aTypeError exception. - Return result.
- Let result be ?
- Perform ?
RequireInternalSlot (R, [[RegExpMatcher]]). - Return ?
RegExpBuiltinExec (R, S).
If a callable
22.2.7.2 RegExpBuiltinExec ( R, S )
The abstract operation RegExpBuiltinExec takes arguments R (an initialized RegExp
instance)
and S (a String) and returns either a
- Let length be the length of S.
- Let lastIndex be
ℝ (?ToLength (?Get (R,"lastIndex" ))). - Let flags be R.[[OriginalFlags]].
- If flags contains
"g" , let global betrue ; else let global befalse . - If flags contains
"y" , let sticky betrue ; else let sticky befalse . - If flags contains
"d" , let hasIndices betrue ; else let hasIndices befalse . - If global is
false and sticky isfalse , set lastIndex to 0. - Let matcher be R.[[RegExpMatcher]].
- If flags contains
"u" or flags contains"v" , let fullUnicode betrue ; else let fullUnicode befalse . - Let matchSucceeded be
false . - If fullUnicode is
true , let input beStringToCodePoints (S). Otherwise, let input be aList whose elements are the code units that are the elements of S. - NOTE: Each element of input is considered to be a character.
- Repeat, while matchSucceeded is
false ,- If lastIndex > length, then
- If global is
true or sticky istrue , then- Perform ?
Set (R,"lastIndex" ,+0 𝔽,true ).
- Perform ?
- Return
null .
- If global is
- Let inputIndex be the index into input of the character that was obtained from element lastIndex of S.
- Let r be matcher(input, inputIndex).
- If r is
failure , then- If sticky is
true , then- Perform ?
Set (R,"lastIndex" ,+0 𝔽,true ). - Return
null .
- Perform ?
- Set lastIndex to
AdvanceStringIndex (S, lastIndex, fullUnicode).
- If sticky is
- Else,
Assert : r is aMatchState .- Set matchSucceeded to
true .
- If lastIndex > length, then
- Let e be r.[[EndIndex]].
- If fullUnicode is
true , set e toGetStringIndex (S, e). - If global is
true or sticky istrue , then - Let n be the number of elements in r.[[Captures]].
Assert : n = R.[[RegExpRecord]].[[CapturingGroupsCount]].Assert : n < 232 - 1.- Let A be !
ArrayCreate (n + 1). Assert : Themathematical value of A's"length" property is n + 1.- Perform !
CreateDataPropertyOrThrow (A,"index" ,𝔽 (lastIndex)). - Perform !
CreateDataPropertyOrThrow (A,"input" , S). - Let match be the
Match Record { [[StartIndex]]: lastIndex, [[EndIndex]]: e }. - Let indices be a new empty
List . - Let groupNames be a new empty
List . - Append match to indices.
- Let matchedSubstr be
GetMatchString (S, match). - Perform !
CreateDataPropertyOrThrow (A,"0" , matchedSubstr). - If R contains any
GroupName , then- Let groups be
OrdinaryObjectCreate (null ). - Let hasGroups be
true .
- Let groups be
- Else,
- Let groups be
undefined . - Let hasGroups be
false .
- Let groups be
- Perform !
CreateDataPropertyOrThrow (A,"groups" , groups). - For each
integer i such that 1 ≤ i ≤ n, in ascending order, do- Let captureI be ith element of r.[[Captures]].
- If captureI is
undefined , then- Let capturedValue be
undefined . - Append
undefined to indices.
- Let capturedValue be
- Else,
- Let captureStart be captureI.[[StartIndex]].
- Let captureEnd be captureI.[[EndIndex]].
- If fullUnicode is
true , then- Set captureStart to
GetStringIndex (S, captureStart). - Set captureEnd to
GetStringIndex (S, captureEnd).
- Set captureStart to
- Let capture be the
Match Record { [[StartIndex]]: captureStart, [[EndIndex]]: captureEnd }. - Let capturedValue be
GetMatchString (S, capture). - Append capture to indices.
- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (i)), capturedValue). - If the ith capture of R
was
defined with a
GroupName , then- Let s be the
CapturingGroupName of thatGroupName . - Perform !
CreateDataPropertyOrThrow (groups, s, capturedValue). - Append s to groupNames.
- Let s be the
- Else,
- Append
undefined to groupNames.
- Append
- If hasIndices is
true , then- Let indicesArray be
MakeMatchIndicesIndexPairArray (S, indices, groupNames, hasGroups). - Perform !
CreateDataPropertyOrThrow (A,"indices" , indicesArray).
- Let indicesArray be
- Return A.
22.2.7.3 AdvanceStringIndex ( S, index, unicode )
The abstract operation AdvanceStringIndex takes arguments S (a String), index
(a
non-negative
Assert : index ≤ 253 - 1.- If unicode is
false , return index + 1. - Let length be the length of S.
- If index + 1 ≥ length, return index + 1.
- Let cp be
CodePointAt (S, index). - Return index + cp.[[CodeUnitCount]].
22.2.7.4 GetStringIndex ( S, codePointIndex )
The abstract operation GetStringIndex takes arguments S (a String) and
codePointIndex (a non-negative
- If S is the empty String, return 0.
- Let len be the length of S.
- Let codeUnitCount be 0.
- Let codePointCount be 0.
- Repeat, while codeUnitCount < len,
- If codePointCount = codePointIndex, return codeUnitCount.
- Let cp be
CodePointAt (S, codeUnitCount). - Set codeUnitCount to codeUnitCount + cp.[[CodeUnitCount]].
- Set codePointCount to codePointCount + 1.
- Return len.
22.2.7.5 Match Records
A Match Record is a
Match Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[StartIndex]] | a non-negative |
The number of code units from the start of a string at which the match begins (inclusive). |
| [[EndIndex]] | an |
The number of code units from the start of a string at which the match ends (exclusive). |
22.2.7.6 GetMatchString ( S, match )
The abstract operation GetMatchString takes arguments S (a String) and match (a
22.2.7.7 GetMatchIndexPair ( S, match )
The abstract operation GetMatchIndexPair takes arguments S (a String) and match
(a
Assert : match.[[StartIndex]] ≤ match.[[EndIndex]] ≤ the length of S.- Return
CreateArrayFromList («𝔽 (match.[[StartIndex]]),𝔽 (match.[[EndIndex]]) »).
22.2.7.8 MakeMatchIndicesIndexPairArray ( S, indices, groupNames, hasGroups )
The abstract operation MakeMatchIndicesIndexPairArray takes arguments S (a String),
indices (a
- Let n be the number of elements in indices.
Assert : n < 232 - 1.Assert : groupNames has n - 1 elements.- NOTE: The groupNames
List contains elements aligned with the indicesList starting at indices[1]. - Let A be !
ArrayCreate (n). - If hasGroups is
true , then- Let groups be
OrdinaryObjectCreate (null ).
- Let groups be
- Else,
- Let groups be
undefined .
- Let groups be
- Perform !
CreateDataPropertyOrThrow (A,"groups" , groups). - For each
integer i such that 0 ≤ i < n, in ascending order, do- Let matchIndices be indices[i].
- If matchIndices is not
undefined , then- Let matchIndexPair be
GetMatchIndexPair (S, matchIndices).
- Let matchIndexPair be
- Else,
- Let matchIndexPair be
undefined .
- Let matchIndexPair be
- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (i)), matchIndexPair). - If i > 0 and
groupNames[i
- 1] is not
undefined , thenAssert : groups is notundefined .- Perform !
CreateDataPropertyOrThrow (groups, groupNames[i - 1], matchIndexPair).
- Return A.
22.2.8 Properties of RegExp Instances
RegExp instances are
Prior to ECMAScript 2015, RegExp instances were specified as having the own RegExp.prototype.
RegExp instances also have the following property:
22.2.8.1 lastIndex
The value of the
22.2.9 RegExp String Iterator Objects
A RegExp String Iterator is an object, that represents a specific iteration over some specific String
instance object, matching against some specific RegExp instance object. There is not a named
22.2.9.1 CreateRegExpStringIterator ( R, S, global, fullUnicode )
The abstract operation CreateRegExpStringIterator takes arguments R (an Object), S (a String), global (a Boolean), and fullUnicode (a Boolean) and returns a Generator. It performs the following steps when called:
- Let closure be a new
Abstract Closure with no parameters that captures R, S, global, and fullUnicode and performs the following steps when called:- Repeat,
- Let match be ?
RegExpExec (R, S). - If match is
null , returnundefined . - If global is
false , then- Perform ?
GeneratorYield (CreateIterResultObject (match,false )). - Return
undefined .
- Perform ?
- Let matchStr be ?
ToString (?Get (match,"0" )). - If matchStr is the empty String, then
- Perform ?
GeneratorYield (CreateIterResultObject (match,false )).
- Let match be ?
- Repeat,
- Return
CreateIteratorFromClosure (closure,"%RegExpStringIteratorPrototype%" ,%RegExpStringIteratorPrototype% ).
22.2.9.2 The %RegExpStringIteratorPrototype% Object
The %RegExpStringIteratorPrototype% object:
- has properties that are inherited by all RegExp String Iterator Objects.
- is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%IteratorPrototype% . - has the following properties:
22.2.9.2.1 %RegExpStringIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%RegExpStringIteratorPrototype%" ).
22.2.9.2.2 %RegExpStringIteratorPrototype% [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
23 Indexed Collections
23.1 Array Objects
Arrays are
23.1.1 The Array Constructor
The Array
- is %Array%.
- is the initial value of the
"Array" property of theglobal object . - creates and initializes a new Array when called as a
constructor . - also creates and initializes a new Array when called as a function rather than as a
constructor . Thus the function callArray(…)is equivalent to the object creation expressionnew Array(…)with the same arguments. - is a function whose behaviour differs based upon the number and types of its arguments.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the exotic Array behaviour must include asupercall to the Arrayconstructor to initialize subclass instances that areArray exotic objects . However, most of theArray.prototypemethods are generic methods that are not dependent upon theirthis value being anArray exotic object .
23.1.1.1 Array ( ...values )
This function performs the following steps when called:
- If NewTarget is
undefined , let newTarget be theactive function object ; else let newTarget be NewTarget. - Let proto be ?
GetPrototypeFromConstructor (newTarget,"%Array.prototype%" ). - Let numberOfArgs be the number of elements in values.
- If numberOfArgs = 0, then
- Return !
ArrayCreate (0, proto).
- Return !
- Else if numberOfArgs = 1, then
- Let len be values[0].
- Let array be !
ArrayCreate (0, proto). - If len
is not a Number , then- Perform !
CreateDataPropertyOrThrow (array,"0" , len). - Let intLen be
1 𝔽.
- Perform !
- Else,
- Let intLen be !
ToUint32 (len). - If
SameValueZero (intLen, len) isfalse , throw aRangeError exception.
- Let intLen be !
- Perform !
Set (array,"length" , intLen,true ). - Return array.
- Else,
Assert : numberOfArgs ≥ 2.- Let array be ?
ArrayCreate (numberOfArgs, proto). - Let k be 0.
- Repeat, while k < numberOfArgs,
- Let Pk be !
ToString (𝔽 (k)). - Let itemK be values[k].
- Perform !
CreateDataPropertyOrThrow (array, Pk, itemK). - Set k to k + 1.
- Let Pk be !
Assert : Themathematical value of array's"length" property is numberOfArgs.- Return array.
23.1.2 Properties of the Array Constructor
The Array
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is1 𝔽. - has the following properties:
23.1.2.1 Array.from ( items [ , mapfn [ , thisArg ] ] )
This method performs the following steps when called:
- Let C be the
this value. - If mapfn is
undefined , then- Let mapping be
false .
- Let mapping be
- Else,
- If
IsCallable (mapfn) isfalse , throw aTypeError exception. - Let mapping be
true .
- If
- Let usingIterator be ?
GetMethod (items,@@iterator ). - If usingIterator is not
undefined , then- If
IsConstructor (C) istrue , then- Let A be ?
Construct (C).
- Let A be ?
- Else,
- Let A be !
ArrayCreate (0).
- Let A be !
- Let iteratorRecord be ?
GetIteratorFromMethod (items, usingIterator). - Let k be 0.
- Repeat,
- If k ≥ 253 - 1, then
- Let error be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iteratorRecord, error).
- Let error be
- Let Pk be !
ToString (𝔽 (k)). - Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , then - If mapping is
true , then- Let mappedValue be
Completion (Call (mapfn, thisArg, « next,𝔽 (k) »)). IfAbruptCloseIterator (mappedValue, iteratorRecord).
- Let mappedValue be
- Else,
- Let mappedValue be next.
- Let defineStatus be
Completion (CreateDataPropertyOrThrow (A, Pk, mappedValue)). IfAbruptCloseIterator (defineStatus, iteratorRecord).- Set k to k + 1.
- If k ≥ 253 - 1, then
- If
- NOTE: items is not an Iterable so assume it is an
array-like object . - Let arrayLike be !
ToObject (items). - Let len be ?
LengthOfArrayLike (arrayLike). - If
IsConstructor (C) istrue , then - Else,
- Let A be ?
ArrayCreate (len).
- Let A be ?
- Let k be 0.
- Repeat, while k < len,
- Perform ?
Set (A,"length" ,𝔽 (len),true ). - Return A.
This method is an intentionally generic factory method; it does not require that its
23.1.2.2 Array.isArray ( arg )
This function performs the following steps when called:
- Return ?
IsArray (arg).
23.1.2.3 Array.of ( ...items )
This method performs the following steps when called:
- Let len be the number of elements in items.
- Let lenNumber be
𝔽 (len). - Let C be the
this value. - If
IsConstructor (C) istrue , then- Let A be ?
Construct (C, « lenNumber »).
- Let A be ?
- Else,
- Let A be ?
ArrayCreate (len).
- Let A be ?
- Let k be 0.
- Repeat, while k < len,
- Let kValue be items[k].
- Let Pk be !
ToString (𝔽 (k)). - Perform ?
CreateDataPropertyOrThrow (A, Pk, kValue). - Set k to k + 1.
- Perform ?
Set (A,"length" , lenNumber,true ). - Return A.
This method is an intentionally generic factory method; it does not require that its
23.1.2.4 Array.prototype
The value of Array.prototype is the
This property has the attributes { [[Writable]]:
23.1.2.5 get Array [ @@species ]
Array[@@species] is an
- Return the
this value.
The value of the
Array prototype methods normally use their
23.1.3 Properties of the Array Prototype Object
The Array prototype object:
- is %Array.prototype%.
- is an
Array exotic object and has the internal methods specified for such objects. - has a
"length" property whose initial value is+0 𝔽 and whose attributes are { [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }. - has a [[Prototype]] internal slot whose value is
%Object.prototype% .
The Array prototype object is specified to be an
23.1.3.1 Array.prototype.at ( index )
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeIndex be ?
ToIntegerOrInfinity (index). - If relativeIndex ≥ 0, then
- Let k be relativeIndex.
- Else,
- Let k be len + relativeIndex.
- If k < 0 or k ≥ len,
return
undefined . - Return ?
Get (O, !ToString (𝔽 (k))).
23.1.3.2 Array.prototype.concat ( ...items )
This method returns an array containing the array elements of the object followed by the array elements of each argument.
It performs the following steps when called:
- Let O be ?
ToObject (this value). - Let A be ?
ArraySpeciesCreate (O, 0). - Let n be 0.
- Prepend O to items.
- For each element E of items, do
- Let spreadable be ?
IsConcatSpreadable (E). - If spreadable is
true , then- Let len be ?
LengthOfArrayLike (E). - If n + len > 253 - 1, throw a
TypeError exception. - Let k be 0.
- Repeat, while k < len,
- Let Pk be !
ToString (𝔽 (k)). - Let exists be ?
HasProperty (E, Pk). - If exists is
true , then- Let subElement be ?
Get (E, Pk). - Perform ?
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), subElement).
- Let subElement be ?
- Set n to n + 1.
- Set k to k + 1.
- Let Pk be !
- Let len be ?
- Else,
- NOTE: E is added as a single item rather than spread.
- If n ≥ 253 - 1, throw a
TypeError exception. - Perform ?
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), E). - Set n to n + 1.
- Let spreadable be ?
- Perform
?
Set (A,"length" ,𝔽 (n),true ). - Return A.
The
The explicit setting of the
This method is intentionally generic; it does not require that its
23.1.3.2.1 IsConcatSpreadable ( O )
The abstract operation IsConcatSpreadable takes argument O (an
- If O
is not an Object , returnfalse . - Let spreadable be ?
Get (O,@@isConcatSpreadable ). - If spreadable is not
undefined , returnToBoolean (spreadable). - Return ?
IsArray (O).
23.1.3.3 Array.prototype.constructor
The initial value of Array.prototype.constructor is
23.1.3.4 Array.prototype.copyWithin ( target, start [ , end ] )
The end argument is optional. If it is not provided, the length of the
If target is negative, it is treated as
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeTarget be ?
ToIntegerOrInfinity (target). - If relativeTarget = -∞, let to be 0.
- Else if relativeTarget < 0, let to
be
max (len + relativeTarget, 0). - Else, let to be
min (relativeTarget, len). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let from be 0.
- Else if relativeStart < 0, let from
be
max (len + relativeStart, 0). - Else, let from be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let final be 0.
- Else if relativeEnd < 0, let final
be
max (len + relativeEnd, 0). - Else, let final be
min (relativeEnd, len). - Let count be
min (final - from, len - to). - If from < to and to <
from + count, then
- Let direction be -1.
- Set from to from + count - 1.
- Set to to to + count - 1.
- Else,
- Let direction be 1.
- Repeat, while count > 0,
- Let fromKey be !
ToString (𝔽 (from)). - Let toKey be !
ToString (𝔽 (to)). - Let fromPresent be ?
HasProperty (O, fromKey). - If fromPresent is
true , then - Else,
Assert : fromPresent isfalse .- Perform ?
DeletePropertyOrThrow (O, toKey).
- Set from to from + direction.
- Set to to to + direction.
- Set count to count - 1.
- Let fromKey be !
- Return O.
This method is intentionally generic; it does not require that its
23.1.3.5 Array.prototype.entries ( )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Return
CreateArrayIterator (O,key+value ).
23.1.3.6 Array.prototype.every ( callbackfn [ , thisArg ] )
callbackfn should be a function that accepts three arguments and returns a value that
is
coercible to a Boolean value. every calls callbackfn once for each element
present in the array, in ascending order, until it finds one where callbackfn returns
every immediately returns
every will return
If a thisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
every does not directly mutate the object on which it is called but the object may
be
mutated by the calls to callbackfn.
The range of elements processed by every is set before the first call to
callbackfn. Elements which are appended to the array after the call to
every
begins will not be visited by callbackfn. If existing elements of the array are
changed,
their value as passed to callbackfn will be the value at the time every
visits
them; elements that are deleted after the call to every begins and before being
visited
are not visited. every acts like the "for all" quantifier in mathematics. In
particular,
for an empty array, it returns
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Let k be 0.
- Repeat, while k < len,
- Return
true .
This method is intentionally generic; it does not require that its
23.1.3.7 Array.prototype.fill ( value [ , start [ , end ] ] )
The start argument is optional. If it is not provided,
The end argument is optional. If it is not provided, the length of the
If start is negative, it is treated as
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let k be 0.
- Else if relativeStart < 0, let k be
max (len + relativeStart, 0). - Else, let k be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let final be 0.
- Else if relativeEnd < 0, let final
be
max (len + relativeEnd, 0). - Else, let final be
min (relativeEnd, len). - Repeat, while k < final,
- Return O.
This method is intentionally generic; it does not require that its
23.1.3.8 Array.prototype.filter ( callbackfn [ , thisArg ] )
callbackfn should be a function that accepts three arguments and returns a value that
is
coercible to a Boolean value. filter calls callbackfn once for each
element
in
the array, in ascending order, and constructs a new array of all the values for which
callbackfn returns
If a thisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
filter does not directly mutate the object on which it is called but the object may
be
mutated by the calls to callbackfn.
The range of elements processed by filter is set before the first call to
callbackfn. Elements which are appended to the array after the call to
filter
begins will not be visited by callbackfn. If existing elements of the array are changed
their value as passed to callbackfn will be the value at the time filter
visits them; elements that are deleted after the call to filter begins and before
being
visited are not visited.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Let A be ?
ArraySpeciesCreate (O, 0). - Let k be 0.
- Let to be 0.
- Repeat, while k < len,
- Let Pk be !
ToString (𝔽 (k)). - Let kPresent be ?
HasProperty (O, Pk). - If kPresent is
true , then - Set k to k + 1.
- Let Pk be !
- Return A.
This method is intentionally generic; it does not require that its
23.1.3.9 Array.prototype.find ( predicate [ , thisArg ] )
This method calls predicate once for each element of the array, in ascending index
order,
until it finds one where predicate returns a value that coerces to
find immediately returns that element value. Otherwise,
find returns
See
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let findRec be ?
FindViaPredicate (O, len,ascending , predicate, thisArg). - Return findRec.[[Value]].
This method is intentionally generic; it does not require that its
23.1.3.10 Array.prototype.findIndex ( predicate [ , thisArg ] )
This method calls predicate once for each element of the array, in ascending index
order,
until it finds one where predicate returns a value that coerces to
findIndex immediately returns the index of that element
value. Otherwise, findIndex returns -1.
See
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let findRec be ?
FindViaPredicate (O, len,ascending , predicate, thisArg). - Return findRec.[[Index]].
This method is intentionally generic; it does not require that its
23.1.3.11 Array.prototype.findLast ( predicate [ , thisArg ] )
This method calls predicate once for each element of the array, in descending index
order,
until it finds one where predicate returns a value that coerces to
findLast immediately returns that element value.
Otherwise,
findLast returns
See
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let findRec be ?
FindViaPredicate (O, len,descending , predicate, thisArg). - Return findRec.[[Value]].
This method is intentionally generic; it does not require that its
23.1.3.12 Array.prototype.findLastIndex ( predicate [ , thisArg ] )
This method calls predicate once for each element of the array, in descending index
order,
until it finds one where predicate returns a value that coerces to
findLastIndex immediately returns the index of that
element
value. Otherwise, findLastIndex returns -1.
See
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let findRec be ?
FindViaPredicate (O, len,descending , predicate, thisArg). - Return findRec.[[Index]].
This method is intentionally generic; it does not require that its
23.1.3.12.1 FindViaPredicate ( O, len, direction, predicate, thisArg )
The abstract operation FindViaPredicate takes arguments O (an Object), len (a
non-negative
O should be an
predicate should be a function. When called for an element of the array, it is passed three arguments: the value of the element, the index of the element, and the object being traversed. Its return value will be coerced to a Boolean value.
thisArg will be used as the
This operation does not directly mutate the object on which it is called, but the object may be mutated by the calls to predicate.
The range of elements processed is set before the first call to predicate, just before
the
traversal begins. Elements that are appended to the array after this will not be visited by
predicate. If existing elements of the array are changed, their value as passed to
predicate will be the value at the time that this operation visits them. Elements that
are
deleted after traversal begins and before being visited are still visited and are either looked up
from
the prototype or are
It performs the following steps when called:
- If
IsCallable (predicate) isfalse , throw aTypeError exception. - If direction is
ascending , then - Else,
- For each
integer k of indices, do- Let Pk be !
ToString (𝔽 (k)). - NOTE: If O is a
TypedArray , the following invocation ofGet will return anormal completion . - Let kValue be ?
Get (O, Pk). - Let testResult be ?
Call (predicate, thisArg, « kValue,𝔽 (k), O »). - If
ToBoolean (testResult) istrue , return theRecord { [[Index]]:𝔽 (k), [[Value]]: kValue }.
- Let Pk be !
- Return the
Record { [[Index]]:-1 𝔽, [[Value]]:undefined }.
23.1.3.13 Array.prototype.flat ( [ depth ] )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let sourceLen be ?
LengthOfArrayLike (O). - Let depthNum be 1.
- If depth is not
undefined , then- Set depthNum to ?
ToIntegerOrInfinity (depth). - If depthNum < 0, set depthNum to 0.
- Set depthNum to ?
- Let A be ?
ArraySpeciesCreate (O, 0). - Perform ?
FlattenIntoArray (A, O, sourceLen, 0, depthNum). - Return A.
23.1.3.13.1 FlattenIntoArray ( target, source, sourceLen, start, depth [ , mapperFunction [ , thisArg ] ] )
The abstract operation FlattenIntoArray takes arguments target (an Object),
source (an Object), sourceLen (a non-negative
Assert : If mapperFunction is present, thenIsCallable (mapperFunction) istrue , thisArg is present, and depth is 1.- Let targetIndex be start.
- Let sourceIndex be
+0 𝔽. - Repeat, while
ℝ (sourceIndex) < sourceLen,- Let P be !
ToString (sourceIndex). - Let exists be ?
HasProperty (source, P). - If exists is
true , then- Let element be ?
Get (source, P). - If mapperFunction is present, then
- Set element to ?
Call (mapperFunction, thisArg, « element, sourceIndex, source »).
- Set element to ?
- Let shouldFlatten be
false . - If depth > 0, then
- Set shouldFlatten to
?
IsArray (element).
- Set shouldFlatten to
?
- If shouldFlatten is
true , then- If depth = +∞, let newDepth be +∞.
- Else, let newDepth be depth - 1.
- Let elementLen be ?
LengthOfArrayLike (element). - Set targetIndex to ?
FlattenIntoArray (target, element, elementLen, targetIndex, newDepth).
- Else,
- If targetIndex ≥ 253 - 1, throw a
TypeError exception. - Perform ?
CreateDataPropertyOrThrow (target, !ToString (𝔽 (targetIndex)), element). - Set targetIndex to targetIndex + 1.
- If targetIndex ≥ 253 - 1, throw a
- Let element be ?
- Set sourceIndex to sourceIndex +
1 𝔽.
- Let P be !
- Return targetIndex.
23.1.3.14 Array.prototype.flatMap ( mapperFunction [ , thisArg ] )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let sourceLen be ?
LengthOfArrayLike (O). - If
IsCallable (mapperFunction) isfalse , throw aTypeError exception. - Let A be ?
ArraySpeciesCreate (O, 0). - Perform ?
FlattenIntoArray (A, O, sourceLen, 0, 1, mapperFunction, thisArg). - Return A.
23.1.3.15 Array.prototype.forEach ( callbackfn [ , thisArg ] )
callbackfn should be a function that accepts three arguments. forEach
calls
callbackfn once for each element present in the array, in ascending order.
callbackfn is called only for elements of the array which actually exist; it is not
called
for missing elements of the array.
If a thisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
forEach does not directly mutate the object on which it is called but the object may
be
mutated by the calls to callbackfn.
The range of elements processed by forEach is set before the first call to
callbackfn. Elements which are appended to the array after the call to
forEach
begins will not be visited by callbackfn. If existing elements of the array are
changed,
their value as passed to callbackfn will be the value at the time forEach
visits them; elements that are deleted after the call to forEach begins and before
being
visited are not visited.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Let k be 0.
- Repeat, while k < len,
- Return
undefined .
This method is intentionally generic; it does not require that its
23.1.3.16 Array.prototype.includes ( searchElement [ , fromIndex ] )
This method compares searchElement to the elements of the array, in ascending order,
using
the
The optional second argument fromIndex defaults to
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If len = 0, return
false . - Let n be ?
ToIntegerOrInfinity (fromIndex). Assert : If fromIndex isundefined , then n is 0.- If n = +∞, return
false . - Else if n = -∞, set n to 0.
- If n ≥ 0, then
- Let k be n.
- Else,
- Let k be len + n.
- If k < 0, set k to 0.
- Repeat, while k < len,
- Let elementK be ?
Get (O, !ToString (𝔽 (k))). - If
SameValueZero (searchElement, elementK) istrue , returntrue . - Set k to k + 1.
- Let elementK be ?
- Return
false .
This method is intentionally generic; it does not require that its
This method intentionally differs from the similar indexOf method in two ways.
First,
it
uses the
23.1.3.17 Array.prototype.indexOf ( searchElement [ , fromIndex ] )
This method compares searchElement to the elements of the array, in ascending order, using
the
The optional second argument fromIndex defaults to
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If len = 0, return
-1 𝔽. - Let n be ?
ToIntegerOrInfinity (fromIndex). Assert : If fromIndex isundefined , then n is 0.- If n = +∞, return
-1 𝔽. - Else if n = -∞, set n to 0.
- If n ≥ 0, then
- Let k be n.
- Else,
- Let k be len + n.
- If k < 0, set k to 0.
- Repeat, while k < len,
- Let kPresent be ?
HasProperty (O, !ToString (𝔽 (k))). - If kPresent is
true , then- Let elementK be ?
Get (O, !ToString (𝔽 (k))). - If
IsStrictlyEqual (searchElement, elementK) istrue , return𝔽 (k).
- Let elementK be ?
- Set k to k + 1.
- Let kPresent be ?
- Return
-1 𝔽.
This method is intentionally generic; it does not require that its
23.1.3.18 Array.prototype.join ( separator )
This method converts the elements of the array to Strings, and then concatenates these Strings, separated by occurrences of the separator. If no separator is provided, a single comma is used as the separator.
It performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If separator is
undefined , let sep be"," . - Else, let sep be ?
ToString (separator). - Let R be the empty String.
- Let k be 0.
- Repeat, while k < len,
- If k > 0, set R to the
string-concatenation of R and sep. - Let element be ?
Get (O, !ToString (𝔽 (k))). - If element is either
undefined ornull , let next be the empty String; otherwise, let next be ?ToString (element). - Set R to the
string-concatenation of R and next. - Set k to k + 1.
- If k > 0, set R to the
- Return R.
This method is intentionally generic; it does not require that its
23.1.3.19 Array.prototype.keys ( )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Return
CreateArrayIterator (O,key ).
23.1.3.20 Array.prototype.lastIndexOf ( searchElement [ , fromIndex ] )
This method compares searchElement to the elements of the array in descending order
using
the
The optional second argument fromIndex defaults to the array's length minus one (i.e.
the
whole array is searched). If it is greater than or equal to the length of the array, the whole
array
will be searched. If it is less than
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If len = 0, return
-1 𝔽. - If fromIndex is present, let n be
?
ToIntegerOrInfinity (fromIndex); else let n be len - 1. - If n = -∞, return
-1 𝔽. - If n ≥ 0, then
- Let k be
min (n, len - 1).
- Let k be
- Else,
- Let k be len + n.
- Repeat, while k ≥ 0,
- Let kPresent be ?
HasProperty (O, !ToString (𝔽 (k))). - If kPresent is
true , then- Let elementK be ?
Get (O, !ToString (𝔽 (k))). - If
IsStrictlyEqual (searchElement, elementK) istrue , return𝔽 (k).
- Let elementK be ?
- Set k to k - 1.
- Let kPresent be ?
- Return
-1 𝔽.
This method is intentionally generic; it does not require that its
23.1.3.21 Array.prototype.map ( callbackfn [ , thisArg ] )
callbackfn should be a function that accepts three arguments. map calls
callbackfn once for each element in the array, in ascending order, and constructs a new
Array from the results. callbackfn is called only for elements of the array which
actually
exist; it is not called for missing elements of the array.
If a thisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
map does not directly mutate the object on which it is called but the object may be
mutated by the calls to callbackfn.
The range of elements processed by map is set before the first call to
callbackfn. Elements which are appended to the array after the call to map
begins will not be visited by callbackfn. If existing elements of the array are
changed,
their value as passed to callbackfn will be the value at the time map
visits
them; elements that are deleted after the call to map begins and before being visited
are
not visited.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Let A be ?
ArraySpeciesCreate (O, len). - Let k be 0.
- Repeat, while k < len,
- Let Pk be !
ToString (𝔽 (k)). - Let kPresent be ?
HasProperty (O, Pk). - If kPresent is
true , then- Let kValue be ?
Get (O, Pk). - Let mappedValue be ?
Call (callbackfn, thisArg, « kValue,𝔽 (k), O »). - Perform ?
CreateDataPropertyOrThrow (A, Pk, mappedValue).
- Let kValue be ?
- Set k to k + 1.
- Let Pk be !
- Return A.
This method is intentionally generic; it does not require that its
23.1.3.22 Array.prototype.pop ( )
This method removes the last element of the array and returns it.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If len = 0, then
- Perform ?
Set (O,"length" ,+0 𝔽,true ). - Return
undefined .
- Perform ?
- Else,
This method is intentionally generic; it does not require that its
23.1.3.23 Array.prototype.push ( ...items )
This method appends the arguments to the end of the array, in the order in which they appear. It returns the new length of the array.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let argCount be the number of elements in items.
- If len + argCount > 253 - 1, throw a
TypeError exception. - For each element E of items, do
- Perform ?
Set (O,"length" ,𝔽 (len),true ). - Return
𝔽 (len).
The
This method is intentionally generic; it does not require that its
23.1.3.24 Array.prototype.reduce ( callbackfn [ , initialValue ] )
callbackfn should be a function that takes four arguments. reduce calls
the
callback, as a function, once for each element after the first element present in the array, in
ascending order.
callbackfn is called with four arguments: the previousValue (value from the
previous call to callbackfn), the currentValue (value of the current
element),
the currentIndex, and the object being traversed. The first time that callback is
called,
the previousValue and currentValue can be one of two values. If an
initialValue was supplied in the call to reduce, then
previousValue
will be initialValue and currentValue will be the first value in the array.
If
no initialValue was supplied, then previousValue will be the first value in
the
array and currentValue will be the second. It is a
reduce does not directly mutate the object on which it is called but the object may
be
mutated by the calls to callbackfn.
The range of elements processed by reduce is set before the first call to
callbackfn. Elements that are appended to the array after the call to
reduce
begins will not be visited by callbackfn. If existing elements of the array are
changed,
their value as passed to callbackfn will be the value at the time reduce
visits them; elements that are deleted after the call to reduce begins and before
being
visited are not visited.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - If len = 0 and initialValue is not
present,
throw a
TypeError exception. - Let k be 0.
- Let accumulator be
undefined . - If initialValue is present, then
- Set accumulator to initialValue.
- Else,
- Let kPresent be
false . - Repeat, while kPresent is
false and k < len,- Let Pk be !
ToString (𝔽 (k)). - Set kPresent to ?
HasProperty (O, Pk). - If kPresent is
true , then- Set accumulator to ?
Get (O, Pk).
- Set accumulator to ?
- Set k to k + 1.
- Let Pk be !
- If kPresent is
false , throw aTypeError exception.
- Let kPresent be
- Repeat, while k < len,
- Return accumulator.
This method is intentionally generic; it does not require that its
23.1.3.25 Array.prototype.reduceRight ( callbackfn [ , initialValue ] )
callbackfn should be a function that takes four arguments. reduceRight
calls
the callback, as a function, once for each element after the first element present in the array,
in
descending order.
callbackfn is called with four arguments: the previousValue (value from the
previous call to callbackfn), the currentValue (value of the current
element),
the currentIndex, and the object being traversed. The first time the function is
called,
the previousValue and currentValue can be one of two values. If an
initialValue was supplied in the call to reduceRight, then
previousValue will be initialValue and currentValue will be the
last
value in the array. If no initialValue was supplied, then previousValue will
be
the last value in the array and currentValue will be the second-to-last value. It is a
reduceRight does not directly mutate the object on which it is called but the object
may
be mutated by the calls to callbackfn.
The range of elements processed by reduceRight is set before the first call to
callbackfn. Elements that are appended to the array after the call to
reduceRight begins will not be visited by callbackfn. If existing elements
of
the array are changed by callbackfn, their value as passed to callbackfn
will
be
the value at the time reduceRight visits them; elements that are deleted after the
call
to reduceRight begins and before being visited are not visited.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - If len = 0 and initialValue is not
present,
throw a
TypeError exception. - Let k be len - 1.
- Let accumulator be
undefined . - If initialValue is present, then
- Set accumulator to initialValue.
- Else,
- Let kPresent be
false . - Repeat, while kPresent is
false and k ≥ 0,- Let Pk be !
ToString (𝔽 (k)). - Set kPresent to ?
HasProperty (O, Pk). - If kPresent is
true , then- Set accumulator to ?
Get (O, Pk).
- Set accumulator to ?
- Set k to k - 1.
- Let Pk be !
- If kPresent is
false , throw aTypeError exception.
- Let kPresent be
- Repeat, while k ≥ 0,
- Return accumulator.
This method is intentionally generic; it does not require that its
23.1.3.26 Array.prototype.reverse ( )
This method rearranges the elements of the array so as to reverse their order. It returns the object as the result of the call.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let middle be
floor (len / 2). - Let lower be 0.
- Repeat, while lower ≠ middle,
- Let upper be len - lower - 1.
- Let upperP be !
ToString (𝔽 (upper)). - Let lowerP be !
ToString (𝔽 (lower)). - Let lowerExists be ?
HasProperty (O, lowerP). - If lowerExists is
true , then- Let lowerValue be ?
Get (O, lowerP).
- Let lowerValue be ?
- Let upperExists be ?
HasProperty (O, upperP). - If upperExists is
true , then- Let upperValue be ?
Get (O, upperP).
- Let upperValue be ?
- If lowerExists is
true and upperExists istrue , then - Else if lowerExists is
false and upperExists istrue , then- Perform ?
Set (O, lowerP, upperValue,true ). - Perform ?
DeletePropertyOrThrow (O, upperP).
- Perform ?
- Else if lowerExists is
true and upperExists isfalse , then- Perform ?
DeletePropertyOrThrow (O, lowerP). - Perform ?
Set (O, upperP, lowerValue,true ).
- Perform ?
- Else,
Assert : lowerExists and upperExists are bothfalse .- NOTE: No action is required.
- Set lower to lower + 1.
- Return O.
This method is intentionally generic; it does not require that its
23.1.3.27 Array.prototype.shift ( )
This method removes the first element of the array and returns it.
It performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If len = 0, then
- Perform ?
Set (O,"length" ,+0 𝔽,true ). - Return
undefined .
- Perform ?
- Let first be ?
Get (O,"0" ). - Let k be 1.
- Repeat, while k < len,
- Let from be !
ToString (𝔽 (k)). - Let to be !
ToString (𝔽 (k - 1)). - Let fromPresent be ?
HasProperty (O, from). - If fromPresent is
true , then - Else,
Assert : fromPresent isfalse .- Perform ?
DeletePropertyOrThrow (O, to).
- Set k to k + 1.
- Let from be !
- Perform ?
DeletePropertyOrThrow (O, !ToString (𝔽 (len - 1))). - Perform ?
Set (O,"length" ,𝔽 (len - 1),true ). - Return first.
This method is intentionally generic; it does not require that its
23.1.3.28 Array.prototype.slice ( start, end )
This method returns an array containing the elements of the array from element start up
to,
but not including, element end (or through the end of the array if end is
It performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let k be 0.
- Else if relativeStart < 0, let k be
max (len + relativeStart, 0). - Else, let k be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let final be 0.
- Else if relativeEnd < 0, let final
be
max (len + relativeEnd, 0). - Else, let final be
min (relativeEnd, len). - Let count be
max (final - k, 0). - Let A be ?
ArraySpeciesCreate (O, count). - Let n be 0.
- Repeat, while k < final,
- Let Pk be !
ToString (𝔽 (k)). - Let kPresent be ?
HasProperty (O, Pk). - If kPresent is
true , then- Let kValue be ?
Get (O, Pk). - Perform ?
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), kValue).
- Let kValue be ?
- Set k to k + 1.
- Set n to n + 1.
- Let Pk be !
- Perform
?
Set (A,"length" ,𝔽 (n),true ). - Return A.
The explicit setting of the
This method is intentionally generic; it does not require that its
23.1.3.29 Array.prototype.some ( callbackfn [ , thisArg ] )
callbackfn should be a function that accepts three arguments and returns a value that
is
coercible to a Boolean value. some calls callbackfn once for each element
present in the array, in ascending order, until it finds one where callbackfn returns
some immediately returns
some returns
If a thisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
some does not directly mutate the object on which it is called but the object may be
mutated by the calls to callbackfn.
The range of elements processed by some is set before the first call to
callbackfn. Elements that are appended to the array after the call to some
begins will not be visited by callbackfn. If existing elements of the array are
changed,
their value as passed to callbackfn will be the value at the time that
some
visits them; elements that are deleted after the call to some begins and before being
visited are not visited. some acts like the "exists" quantifier in mathematics. In
particular, for an empty array, it returns
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Let k be 0.
- Repeat, while k < len,
- Return
false .
This method is intentionally generic; it does not require that its
23.1.3.30 Array.prototype.sort ( comparefn )
This method sorts the elements of this array. The sort must be stable (that is, elements that compare
equal must remain in their original order). If comparefn is not
It performs the following steps when called:
- If comparefn is not
undefined andIsCallable (comparefn) isfalse , throw aTypeError exception. - Let obj be ?
ToObject (this value). - Let len be
?
LengthOfArrayLike (obj). - Let SortCompare be a new
Abstract Closure with parameters (x, y) that captures comparefn and performs the following steps when called:- Return ?
CompareArrayElements (x, y, comparefn).
- Return ?
- Let
sortedList
be ?
SortIndexedProperties (obj, len, SortCompare,skip-holes ). - Let itemCount be the number of elements in sortedList.
- Let j be 0.
- Repeat, while j < itemCount,
- NOTE: The call to
SortIndexedProperties in step5 usesskip-holes . The remaining indices are deleted to preserve the number of holes that were detected and excluded from the sort. - Repeat, while j < len,
- Perform ?
DeletePropertyOrThrow (obj, !ToString (𝔽 (j))). - Set j to j + 1.
- Perform ?
- Return obj.
Because non-existent property values always compare greater than
Method calls performed by the
This method is intentionally generic; it does not require that its
23.1.3.30.1 SortIndexedProperties ( obj, len, SortCompare, holes )
The abstract operation SortIndexedProperties takes arguments obj (an Object),
len
(a non-negative
- Let items be a new empty
List . - Let k be 0.
- Repeat, while k < len,
- Let Pk be !
ToString (𝔽 (k)). - If holes is
skip-holes , then- Let kRead be ?
HasProperty (obj, Pk).
- Let kRead be ?
- Else,
Assert : holes isread-through-holes .- Let kRead be
true .
- If kRead is
true , then- Let kValue be ?
Get (obj, Pk). - Append kValue to items.
- Let kValue be ?
- Set k to k + 1.
- Let Pk be !
- Sort items using an
implementation-defined sequence of calls to SortCompare. If any such call returns anabrupt completion , stop before performing any further calls to SortCompare and return thatCompletion Record . - Return items.
The sort order is the ordering of items after
completion of step
Unless the
-
There must be some mathematical permutation π of the non-negative
integers less than itemCount, such that for every non-negativeinteger j less than itemCount, the elementold[j] is exactly the same asnew[π(j)] . -
Then for all non-negative
integers j and k, each less than itemCount, ifℝ (SortCompare(old[j], old[k])) < 0π(j) < π(k) .
Here the notation
An abstract closure or function comparator is a consistent comparator for a set of values S if all of the
requirements
below are met for all values a, b, and c (possibly the same value)
in
the set S: The notation
-
Calling comparator(a, b) always returns the same value
v
when given a specific pair of values a and b as its two arguments.
Furthermore,
v
is a Number , and v is notNaN . Note that this implies that exactly one of a <C b, a =C b, and a >C b will be true for a given pair of a and b. - Calling comparator(a, b) does not modify obj or any object on obj's prototype chain.
- a =C a (reflexivity)
- If a =C b, then b =C a (symmetry)
- If a =C b and b =C c, then a =C c (transitivity of =C)
- If a <C b and b <C c, then a <C c (transitivity of <C)
- If a >C b and b >C c, then a >C c (transitivity of >C)
The above conditions are necessary and sufficient to ensure that comparator divides the set S into equivalence classes and that these equivalence classes are totally ordered.
23.1.3.30.2 CompareArrayElements ( x, y, comparefn )
The abstract operation CompareArrayElements takes arguments x (an
- If x and y are both
undefined , return+0 𝔽. - If x is
undefined , return1 𝔽. - If y is
undefined , return-1 𝔽. - If comparefn is not
undefined , then - Let xString be
?
ToString (x). - Let yString be
?
ToString (y). - Let xSmaller be !
IsLessThan (xString, yString,true ). - If xSmaller is
true , return-1 𝔽. - Let ySmaller be !
IsLessThan (yString, xString,true ). - If ySmaller is
true , return1 𝔽. - Return
+0 𝔽.
23.1.3.31 Array.prototype.splice ( start, deleteCount, ...items )
This method deletes the deleteCount elements of the array starting at
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let actualStart be 0.
- Else if relativeStart < 0, let
actualStart be
max (len + relativeStart, 0). - Else, let actualStart be
min (relativeStart, len). - Let itemCount be the number of elements in items.
- If start is not present, then
- Let actualDeleteCount be 0.
- Else if deleteCount is not present, then
- Let actualDeleteCount be len - actualStart.
- Else,
- Let dc be ?
ToIntegerOrInfinity (deleteCount). - Let actualDeleteCount be the result of
clamping dc between 0 and len - actualStart.
- Let dc be ?
- If len + itemCount -
actualDeleteCount > 253 - 1, throw a
TypeError exception. - Let A be ?
ArraySpeciesCreate (O, actualDeleteCount). - Let k be 0.
- Repeat, while k <
actualDeleteCount,
- Let from be !
ToString (𝔽 (actualStart + k)). - If ?
HasProperty (O, from) istrue , then- Let fromValue be ?
Get (O, from). - Perform ?
CreateDataPropertyOrThrow (A, !ToString (𝔽 (k)), fromValue).
- Let fromValue be ?
- Set k to k + 1.
- Let from be !
- Perform
?
Set (A,"length" ,𝔽 (actualDeleteCount),true ). - If itemCount < actualDeleteCount,
then
- Set k to actualStart.
- Repeat, while k < (len -
actualDeleteCount),
- Let from be !
ToString (𝔽 (k + actualDeleteCount)). - Let to be !
ToString (𝔽 (k + itemCount)). - If ?
HasProperty (O, from) istrue , then - Else,
- Perform ?
DeletePropertyOrThrow (O, to).
- Perform ?
- Set k to k + 1.
- Let from be !
- Set k to len.
- Repeat, while k > (len -
actualDeleteCount + itemCount),
- Perform ?
DeletePropertyOrThrow (O, !ToString (𝔽 (k - 1))). - Set k to k - 1.
- Perform ?
- Else if itemCount >
actualDeleteCount,
then
- Set k to (len - actualDeleteCount).
- Repeat, while k > actualStart,
- Let from be !
ToString (𝔽 (k + actualDeleteCount - 1)). - Let to be !
ToString (𝔽 (k + itemCount - 1)). - If ?
HasProperty (O, from) istrue , then - Else,
- Perform ?
DeletePropertyOrThrow (O, to).
- Perform ?
- Set k to k - 1.
- Let from be !
- Set k to actualStart.
- For each element E of items, do
- Perform
?
Set (O,"length" ,𝔽 (len - actualDeleteCount + itemCount),true ). - Return A.
This method is intentionally generic; it does not require that its
23.1.3.32 Array.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used.
The first edition of ECMA-402 did not include a replacement specification for this method.
The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
This method performs the following steps when called:
- Let array be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (array). - Let separator be the
implementation-defined list-separator String value appropriate for thehost environment 's current locale (such as", " ). - Let R be the empty String.
- Let k be 0.
- Repeat, while k < len,
- If k > 0, then
- Set R to the
string-concatenation of R and separator.
- Set R to the
- Let nextElement be ?
Get (array, !ToString (𝔽 (k))). - If nextElement is neither
undefined nornull , then- Let S be ?
ToString (?Invoke (nextElement,"toLocaleString" )). - Set R to the
string-concatenation of R and S.
- Let S be ?
- Set k to k + 1.
- If k > 0, then
- Return R.
This method converts the elements of the array to Strings using their toLocaleString
methods, and then concatenates these Strings, separated by occurrences of an toString except that
it
is
intended to yield a locale-sensitive result corresponding with conventions of the
This method is intentionally generic; it does not require that its
23.1.3.33 Array.prototype.toReversed ( )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let A be ?
ArrayCreate (len). - Let k be 0.
- Repeat, while k < len,
- Return A.
23.1.3.34 Array.prototype.toSorted ( comparefn )
This method performs the following steps when called:
- If comparefn is not
undefined andIsCallable (comparefn) isfalse , throw aTypeError exception. - Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let A be ?
ArrayCreate (len). - Let SortCompare be a new
Abstract Closure with parameters (x, y) that captures comparefn and performs the following steps when called:- Return ?
CompareArrayElements (x, y, comparefn).
- Return ?
- Let sortedList be ?
SortIndexedProperties (O, len, SortCompare,read-through-holes ). - Let j be 0.
- Repeat, while j < len,
- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (j)), sortedList[j]). - Set j to j + 1.
- Perform !
- Return A.
23.1.3.35 Array.prototype.toSpliced ( start, skipCount, ...items )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart is -∞, let actualStart be 0.
- Else if relativeStart < 0, let
actualStart be
max (len + relativeStart, 0). - Else, let actualStart be
min (relativeStart, len). - Let insertCount be the number of elements in items.
- If start is not present, then
- Let actualSkipCount be 0.
- Else if skipCount is not present, then
- Let actualSkipCount be len - actualStart.
- Else,
- Let sc be ?
ToIntegerOrInfinity (skipCount). - Let actualSkipCount be the result of
clamping sc between 0 and len - actualStart.
- Let sc be ?
- Let newLen be len + insertCount - actualSkipCount.
- If newLen > 253 - 1, throw a
TypeError exception. - Let A be ?
ArrayCreate (newLen). - Let i be 0.
- Let r be actualStart + actualSkipCount.
- Repeat, while i < actualStart,
- Let Pi be !
ToString (𝔽 (i)). - Let iValue be ?
Get (O, Pi). - Perform !
CreateDataPropertyOrThrow (A, Pi, iValue). - Set i to i + 1.
- Let Pi be !
- For each element E of items, do
- Let Pi be !
ToString (𝔽 (i)). - Perform !
CreateDataPropertyOrThrow (A, Pi, E). - Set i to i + 1.
- Let Pi be !
- Repeat, while i < newLen,
- Return A.
23.1.3.36 Array.prototype.toString ( )
This method performs the following steps when called:
- Let array be ?
ToObject (this value). - Let func be ?
Get (array,"join" ). - If
IsCallable (func) isfalse , set func to the intrinsic function %Object.prototype.toString%. - Return ?
Call (func, array).
This method is intentionally generic; it does not require that its
23.1.3.37 Array.prototype.unshift ( ...items )
This method prepends the arguments to the start of the array, such that their order within the array is the same as the order in which they appear in the argument list.
It performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let argCount be the number of elements in items.
- If argCount > 0, then
- If len + argCount > 253 - 1, throw a
TypeError exception. - Let k be len.
- Repeat, while k > 0,
- Let from be !
ToString (𝔽 (k - 1)). - Let to be !
ToString (𝔽 (k + argCount - 1)). - Let fromPresent be ?
HasProperty (O, from). - If fromPresent is
true , then - Else,
Assert : fromPresent isfalse .- Perform ?
DeletePropertyOrThrow (O, to).
- Set k to k - 1.
- Let from be !
- Let j be
+0 𝔽. - For each element E of items, do
- If len + argCount > 253 - 1, throw a
- Perform ?
Set (O,"length" ,𝔽 (len + argCount),true ). - Return
𝔽 (len + argCount).
The
This method is intentionally generic; it does not require that its
23.1.3.38 Array.prototype.values ( )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Return
CreateArrayIterator (O,value ).
23.1.3.39 Array.prototype.with ( index, value )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeIndex be ?
ToIntegerOrInfinity (index). - If relativeIndex ≥ 0, let actualIndex be relativeIndex.
- Else, let actualIndex be len + relativeIndex.
- If actualIndex ≥ len or
actualIndex < 0, throw a
RangeError exception. - Let A be ?
ArrayCreate (len). - Let k be 0.
- Repeat, while k < len,
- Let Pk be !
ToString (𝔽 (k)). - If k is actualIndex, let fromValue be value.
- Else, let fromValue be ?
Get (O, Pk). - Perform !
CreateDataPropertyOrThrow (A, Pk, fromValue). - Set k to k + 1.
- Let Pk be !
- Return A.
23.1.3.40 Array.prototype [ @@iterator ] ( )
The initial value of the
23.1.3.41 Array.prototype [ @@unscopables ]
The initial value of the
- Let unscopableList be
OrdinaryObjectCreate (null ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"at" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"copyWithin" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"entries" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"fill" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"find" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"findIndex" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"findLast" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"findLastIndex" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"flat" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"flatMap" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"includes" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"keys" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"toReversed" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"toSorted" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"toSpliced" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"values" ,true ). - Return unscopableList.
This property has the attributes { [[Writable]]:
The own property names of this object are property names that were not included as standard
properties of Array.prototype prior to the ECMAScript 2015 specification. These names
are
ignored for with statement binding purposes in order to preserve the behaviour of
existing code that might use one of these names as a binding in an outer scope that is shadowed by
a
with statement whose binding object is an Array.
The reason that
23.1.4 Properties of Array Instances
Array instances are
Array instances have a
23.1.4.1 length
The
The
Reducing the value of the
23.1.5 Array Iterator Objects
An Array Iterator is an object, that represents a specific iteration over some specific Array instance
object. There is not a named
23.1.5.1 CreateArrayIterator ( array, kind )
The abstract operation CreateArrayIterator takes arguments array (an Object) and
kind (
- Let closure be a new
Abstract Closure with no parameters that captures kind and array and performs the following steps when called:- Let index be 0.
- Repeat,
- If array has a [[TypedArrayName]] internal slot, then
- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (array,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Let len be
TypedArrayLength (taRecord).
- Let taRecord be
- Else,
- Let len be ?
LengthOfArrayLike (array).
- Let len be ?
- If index ≥ len, return
NormalCompletion (undefined ). - Let indexNumber be
𝔽 (index). - If kind is
key , then- Let result be indexNumber.
- Else,
- Let elementKey be !
ToString (indexNumber). - Let elementValue be ?
Get (array, elementKey). - If kind is
value , then- Let result be elementValue.
- Else,
Assert : kind iskey+value .- Let result be
CreateArrayFromList (« indexNumber, elementValue »).
- Let elementKey be !
- Perform ?
GeneratorYield (CreateIterResultObject (result,false )). - Set index to index + 1.
- If array has a [[TypedArrayName]] internal slot, then
- Return
CreateIteratorFromClosure (closure,"%ArrayIteratorPrototype%" ,%ArrayIteratorPrototype% ).
23.1.5.2 The %ArrayIteratorPrototype% Object
The %ArrayIteratorPrototype% object:
- has properties that are inherited by all Array Iterator Objects.
- is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%IteratorPrototype% . - has the following properties:
23.1.5.2.1 %ArrayIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%ArrayIteratorPrototype%" ).
23.1.5.2.2 %ArrayIteratorPrototype% [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
23.2 TypedArray Objects
A TypedArray presents an array-like view of an underlying binary data buffer (
|
|
Element Type | Element Size | Conversion Operation | Description |
|---|---|---|---|---|
|
Int8Array %Int8Array% |
|
1 |
|
8-bit two's complement signed |
|
Uint8Array %Uint8Array% |
|
1 |
|
8-bit unsigned |
|
Uint8ClampedArray %Uint8ClampedArray% |
|
1 |
|
8-bit unsigned |
|
Int16Array %Int16Array% |
|
2 |
|
16-bit two's complement signed |
|
Uint16Array %Uint16Array% |
|
2 |
|
16-bit unsigned |
|
Int32Array %Int32Array% |
|
4 |
|
32-bit two's complement signed |
|
Uint32Array %Uint32Array% |
|
4 |
|
32-bit unsigned |
|
BigInt64Array %BigInt64Array% |
|
8 |
|
64-bit two's complement signed |
|
BigUint64Array %BigUint64Array% |
|
8 |
|
64-bit unsigned |
|
Float32Array %Float32Array% |
|
4 | 32-bit IEEE floating point | |
|
Float64Array %Float64Array% |
|
8 | 64-bit IEEE floating point |
In the definitions below, references to TypedArray should be replaced with the appropriate
23.2.1 The %TypedArray% Intrinsic Object
The %TypedArray% intrinsic object:
- is a
constructor function object that all of the TypedArrayconstructor objects inherit from. - along with its corresponding prototype object, provides common properties that are inherited by all
TypedArray
constructors and their instances. - does not have a global name or appear as a property of the
global object . - acts as the abstract superclass of the various TypedArray
constructors . - will throw an error when invoked, because it is an abstract class
constructor . The TypedArrayconstructors do not perform asupercall to it.
23.2.1.1 %TypedArray% ( )
This function performs the following steps when called:
- Throw a
TypeError exception.
The
23.2.2 Properties of the %TypedArray% Intrinsic Object
The
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"name" property whose value is"TypedArray" . - has the following properties:
23.2.2.1 %TypedArray%.from ( source [ , mapfn [ , thisArg ] ] )
This method performs the following steps when called:
- Let C be the
this value. - If
IsConstructor (C) isfalse , throw aTypeError exception. - If mapfn is
undefined , then- Let mapping be
false .
- Let mapping be
- Else,
- If
IsCallable (mapfn) isfalse , throw aTypeError exception. - Let mapping be
true .
- If
- Let usingIterator be ?
GetMethod (source,@@iterator ). - If usingIterator is not
undefined , then- Let values be ?
IteratorToList (?GetIteratorFromMethod (source, usingIterator)). - Let len be the number of elements in values.
- Let targetObj be ?
TypedArrayCreateFromConstructor (C, «𝔽 (len) »). - Let k be 0.
- Repeat, while k < len,
Assert : values is now an emptyList .- Return targetObj.
- Let values be ?
- NOTE: source is not an Iterable so assume it is
already an
array-like object . - Let arrayLike be !
ToObject (source). - Let len be ?
LengthOfArrayLike (arrayLike). - Let targetObj be ?
TypedArrayCreateFromConstructor (C, «𝔽 (len) »). - Let k be 0.
- Repeat, while k < len,
- Return targetObj.
23.2.2.2 %TypedArray%.of ( ...items )
This method performs the following steps when called:
- Let len be the number of elements in items.
- Let C be the
this value. - If
IsConstructor (C) isfalse , throw aTypeError exception. - Let newObj be ?
TypedArrayCreateFromConstructor (C, «𝔽 (len) »). - Let k be 0.
- Repeat, while k < len,
- Return newObj.
23.2.2.3 %TypedArray%.prototype
The initial value of .prototype
is the
This property has the attributes { [[Writable]]:
23.2.2.4 get %TypedArray% [ @@species ]
[@@species]
is an
- Return the
this value.
The value of the
23.2.3 Properties of the %TypedArray% Prototype Object
The %TypedArray% prototype object:
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is %TypedArray.prototype%.
- is an
ordinary object . - does not have a [[ViewedArrayBuffer]] or any other of the internal slots that are specific to TypedArray instance objects.
23.2.3.1 %TypedArray%.prototype.at ( index )
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let relativeIndex be ?
ToIntegerOrInfinity (index). - If relativeIndex ≥ 0, then
- Let k be relativeIndex.
- Else,
- Let k be len + relativeIndex.
- If k < 0 or k ≥ len,
return
undefined . - Return !
Get (O, !ToString (𝔽 (k))).
23.2.3.2 get %TypedArray%.prototype.buffer
.prototype.buffer
is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[TypedArrayName]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let buffer be O.[[ViewedArrayBuffer]].
- Return buffer.
23.2.3.3 get %TypedArray%.prototype.byteLength
.prototype.byteLength
is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[TypedArrayName]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - Let size be
TypedArrayByteLength (taRecord). - Return
𝔽 (size).
23.2.3.4 get %TypedArray%.prototype.byteOffset
.prototype.byteOffset
is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[TypedArrayName]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , return+0 𝔽. - Let offset be O.[[ByteOffset]].
- Return
𝔽 (offset).
23.2.3.5 %TypedArray%.prototype.constructor
The initial value of .prototype.constructor
is
23.2.3.6 %TypedArray%.prototype.copyWithin ( target, start [ , end ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.copyWithin as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let relativeTarget be ?
ToIntegerOrInfinity (target). - If relativeTarget = -∞, let targetIndex be 0.
- Else if relativeTarget < 0, let
targetIndex be
max (len + relativeTarget, 0). - Else, let targetIndex be
min (relativeTarget, len). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let startIndex be 0.
- Else if relativeStart < 0, let
startIndex be
max (len + relativeStart, 0). - Else, let startIndex be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let endIndex be 0.
- Else if relativeEnd < 0, let
endIndex
be
max (len + relativeEnd, 0). - Else, let endIndex be
min (relativeEnd, len). - Let count be
min (endIndex - startIndex, len - targetIndex). - If count > 0, then
- NOTE: The copying must be performed in a manner that preserves the bit-level encoding of the source data.
- Let buffer be O.[[ViewedArrayBuffer]].
- Set taRecord to
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Set len to
TypedArrayLength (taRecord). - Let elementSize be
TypedArrayElementSize (O). - Let byteOffset be O.[[ByteOffset]].
- Let bufferByteLimit be (len × elementSize) + byteOffset.
- Let toByteIndex be (targetIndex × elementSize) + byteOffset.
- Let fromByteIndex be (startIndex × elementSize) + byteOffset.
- Let countBytes be count × elementSize.
- If fromByteIndex < toByteIndex
and
toByteIndex < fromByteIndex + countBytes, then
- Let direction be -1.
- Set fromByteIndex to fromByteIndex + countBytes - 1.
- Set toByteIndex to toByteIndex + countBytes - 1.
- Else,
- Let direction be 1.
- Repeat, while countBytes > 0,
- If fromByteIndex <
bufferByteLimit and toByteIndex < bufferByteLimit,
then
- Let value be
GetValueFromBuffer (buffer, fromByteIndex,uint8 ,true ,unordered ). - Perform
SetValueInBuffer (buffer, toByteIndex,uint8 , value,true ,unordered ). - Set fromByteIndex to fromByteIndex + direction.
- Set toByteIndex to toByteIndex + direction.
- Set countBytes to countBytes - 1.
- Let value be
- Else,
- Set countBytes to 0.
- If fromByteIndex <
bufferByteLimit and toByteIndex < bufferByteLimit,
then
- Return O.
23.2.3.7 %TypedArray%.prototype.entries ( )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
ValidateTypedArray (O,seq-cst ). - Return
CreateArrayIterator (O,key+value ).
23.2.3.8 %TypedArray%.prototype.every ( callbackfn [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.every as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Let k be 0.
- Repeat, while k < len,
- Return
true .
This method is not generic. The
23.2.3.9 %TypedArray%.prototype.fill ( value [ , start [ , end ] ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.fill as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If O.[[ContentType]] is
bigint , set value to ?ToBigInt (value). - Otherwise, set value to ?
ToNumber (value). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let startIndex be 0.
- Else if relativeStart < 0, let
startIndex be
max (len + relativeStart, 0). - Else, let startIndex be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let endIndex be 0.
- Else if relativeEnd < 0, let
endIndex
be
max (len + relativeEnd, 0). - Else, let endIndex be
min (relativeEnd, len). - Set taRecord to
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Set len to
TypedArrayLength (taRecord). - Set endIndex to
min (endIndex, len). - Let k be startIndex.
- Repeat, while k < endIndex,
- Return O.
23.2.3.10 %TypedArray%.prototype.filter ( callbackfn [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.filter as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Let kept be a new empty
List . - Let captured be 0.
- Let k be 0.
- Repeat, while k < len,
- Let A be ?
TypedArraySpeciesCreate (O, «𝔽 (captured) »). - Let n be 0.
- For each element e of kept, do
- Return A.
This method is not generic. The
23.2.3.11 %TypedArray%.prototype.find ( predicate [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.find as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let findRec be ?
FindViaPredicate (O, len,ascending , predicate, thisArg). - Return findRec.[[Value]].
This method is not generic. The
23.2.3.12 %TypedArray%.prototype.findIndex ( predicate [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.findIndex as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let findRec be ?
FindViaPredicate (O, len,ascending , predicate, thisArg). - Return findRec.[[Index]].
This method is not generic. The
23.2.3.13 %TypedArray%.prototype.findLast ( predicate [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.findLast as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let findRec be ?
FindViaPredicate (O, len,descending , predicate, thisArg). - Return findRec.[[Value]].
This method is not generic. The
23.2.3.14 %TypedArray%.prototype.findLastIndex ( predicate [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.findLastIndex as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let findRec be ?
FindViaPredicate (O, len,descending , predicate, thisArg). - Return findRec.[[Index]].
This method is not generic. The
23.2.3.15 %TypedArray%.prototype.forEach ( callbackfn [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.forEach as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Let k be 0.
- Repeat, while k < len,
- Return
undefined .
This method is not generic. The
23.2.3.16 %TypedArray%.prototype.includes ( searchElement [ , fromIndex ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.includes as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If len = 0, return
false . - Let n be ?
ToIntegerOrInfinity (fromIndex). Assert : If fromIndex isundefined , then n is 0.- If n = +∞, return
false . - Else if n = -∞, set n to 0.
- If n ≥ 0, then
- Let k be n.
- Else,
- Let k be len + n.
- If k < 0, set k to 0.
- Repeat, while k < len,
- Let elementK be !
Get (O, !ToString (𝔽 (k))). - If
SameValueZero (searchElement, elementK) istrue , returntrue . - Set k to k + 1.
- Let elementK be !
- Return
false .
This method is not generic. The
23.2.3.17 %TypedArray%.prototype.indexOf ( searchElement [ , fromIndex ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.indexOf as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If len = 0, return
-1 𝔽. - Let n be ?
ToIntegerOrInfinity (fromIndex). Assert : If fromIndex isundefined , then n is 0.- If n = +∞, return
-1 𝔽. - Else if n = -∞, set n to 0.
- If n ≥ 0, then
- Let k be n.
- Else,
- Let k be len + n.
- If k < 0, set k to 0.
- Repeat, while k < len,
- Let kPresent be !
HasProperty (O, !ToString (𝔽 (k))). - If kPresent is
true , then- Let elementK be !
Get (O, !ToString (𝔽 (k))). - If
IsStrictlyEqual (searchElement, elementK) istrue , return𝔽 (k).
- Let elementK be !
- Set k to k + 1.
- Let kPresent be !
- Return
-1 𝔽.
This method is not generic. The
23.2.3.18 %TypedArray%.prototype.join ( separator )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.join as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If separator is
undefined , let sep be"," . - Else, let sep be ?
ToString (separator). - Let R be the empty String.
- Let k be 0.
- Repeat, while k < len,
- If k > 0, set R to the
string-concatenation of R and sep. - Let element be !
Get (O, !ToString (𝔽 (k))). - If element is
undefined , let next be the empty String; otherwise, let next be !ToString (element). - Set R to the
string-concatenation of R and next. - Set k to k + 1.
- If k > 0, set R to the
- Return R.
This method is not generic. The
23.2.3.19 %TypedArray%.prototype.keys ( )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
ValidateTypedArray (O,seq-cst ). - Return
CreateArrayIterator (O,key ).
23.2.3.20 %TypedArray%.prototype.lastIndexOf ( searchElement [ , fromIndex ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.lastIndexOf as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If len = 0, return
-1 𝔽. - If fromIndex is present, let n be
?
ToIntegerOrInfinity (fromIndex); else let n be len - 1. - If n = -∞, return
-1 𝔽. - If n ≥ 0, then
- Let k be
min (n, len - 1).
- Let k be
- Else,
- Let k be len + n.
- Repeat, while k ≥ 0,
- Let kPresent be !
HasProperty (O, !ToString (𝔽 (k))). - If kPresent is
true , then- Let elementK be !
Get (O, !ToString (𝔽 (k))). - If
IsStrictlyEqual (searchElement, elementK) istrue , return𝔽 (k).
- Let elementK be !
- Set k to k - 1.
- Let kPresent be !
- Return
-1 𝔽.
This method is not generic. The
23.2.3.21 get %TypedArray%.prototype.length
.prototype.length
is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[TypedArrayName]]). Assert : O has [[ViewedArrayBuffer]] and [[ArrayLength]] internal slots.- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , return+0 𝔽. - Let length be
TypedArrayLength (taRecord). - Return
𝔽 (length).
This function is not generic. The
23.2.3.22 %TypedArray%.prototype.map ( callbackfn [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.map as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Let A be ?
TypedArraySpeciesCreate (O, «𝔽 (len) »). - Let k be 0.
- Repeat, while k < len,
- Return A.
This method is not generic. The
23.2.3.23 %TypedArray%.prototype.reduce ( callbackfn [ , initialValue ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.reduce as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - If len = 0 and initialValue is not
present,
throw a
TypeError exception. - Let k be 0.
- Let accumulator be
undefined . - If initialValue is present, then
- Set accumulator to initialValue.
- Else,
- Repeat, while k < len,
- Return accumulator.
This method is not generic. The
23.2.3.24 %TypedArray%.prototype.reduceRight ( callbackfn [ , initialValue ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.reduceRight as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - If len = 0 and initialValue is not
present,
throw a
TypeError exception. - Let k be len - 1.
- Let accumulator be
undefined . - If initialValue is present, then
- Set accumulator to initialValue.
- Else,
- Repeat, while k ≥ 0,
- Return accumulator.
This method is not generic. The
23.2.3.25 %TypedArray%.prototype.reverse ( )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.reverse as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let middle be
floor (len / 2). - Let lower be 0.
- Repeat, while lower ≠ middle,
- Return O.
This method is not generic. The
23.2.3.26 %TypedArray%.prototype.set ( source [ , offset ] )
This method sets multiple values in this TypedArray, reading the values from source. The details differ based upon the type of source. The optional offset value indicates the first element index in this TypedArray where values are written. If omitted, it is assumed to be 0.
It performs the following steps when called:
- Let target be the
this value. - Perform ?
RequireInternalSlot (target, [[TypedArrayName]]). Assert : target has a [[ViewedArrayBuffer]] internal slot.- Let targetOffset be ?
ToIntegerOrInfinity (offset). - If targetOffset < 0, throw a
RangeError exception. - If source
is an Object that has a [[TypedArrayName]] internal slot, then- Perform ?
SetTypedArrayFromTypedArray (target, targetOffset, source).
- Perform ?
- Else,
- Perform ?
SetTypedArrayFromArrayLike (target, targetOffset, source).
- Perform ?
- Return
undefined .
This method is not generic. The
23.2.3.26.1 SetTypedArrayFromTypedArray ( target, targetOffset, source )
The abstract operation SetTypedArrayFromTypedArray takes arguments target (a
- Let targetBuffer be target.[[ViewedArrayBuffer]].
- Let targetRecord be
MakeTypedArrayWithBufferWitnessRecord (target,seq-cst ). - If
IsTypedArrayOutOfBounds (targetRecord) istrue , throw aTypeError exception. - Let targetLength be
TypedArrayLength (targetRecord). - Let srcBuffer be source.[[ViewedArrayBuffer]].
- Let srcRecord be
MakeTypedArrayWithBufferWitnessRecord (source,seq-cst ). - If
IsTypedArrayOutOfBounds (srcRecord) istrue , throw aTypeError exception. - Let srcLength be
TypedArrayLength (srcRecord). - Let targetType be
TypedArrayElementType (target). - Let targetElementSize be
TypedArrayElementSize (target). - Let targetByteOffset be target.[[ByteOffset]].
- Let srcType be
TypedArrayElementType (source). - Let srcElementSize be
TypedArrayElementSize (source). - Let srcByteOffset be source.[[ByteOffset]].
- If targetOffset = +∞, throw a
RangeError exception. - If srcLength + targetOffset >
targetLength, throw a
RangeError exception. - If target.[[ContentType]]
is not source.[[ContentType]], throw a
TypeError exception. - If
IsSharedArrayBuffer (srcBuffer) istrue ,IsSharedArrayBuffer (targetBuffer) istrue , and srcBuffer.[[ArrayBufferData]] is targetBuffer.[[ArrayBufferData]], let sameSharedArrayBuffer betrue ; otherwise, let sameSharedArrayBuffer befalse . - If
SameValue (srcBuffer, targetBuffer) istrue or sameSharedArrayBuffer istrue , then- Let srcByteLength be
TypedArrayByteLength (srcRecord). - Set srcBuffer to ?
CloneArrayBuffer (srcBuffer, srcByteOffset, srcByteLength). - Let srcByteIndex be 0.
- Let srcByteLength be
- Else,
- Let srcByteIndex be srcByteOffset.
- Let targetByteIndex be (targetOffset × targetElementSize) + targetByteOffset.
- Let limit be targetByteIndex + (targetElementSize × srcLength).
- If srcType is targetType, then
- NOTE: The transfer must be performed in a manner that preserves the bit-level encoding of the source data.
- Repeat, while targetByteIndex <
limit,
- Let value be
GetValueFromBuffer (srcBuffer, srcByteIndex,uint8 ,true ,unordered ). - Perform
SetValueInBuffer (targetBuffer, targetByteIndex,uint8 , value,true ,unordered ). - Set srcByteIndex to srcByteIndex + 1.
- Set targetByteIndex to targetByteIndex + 1.
- Let value be
- Else,
- Repeat, while targetByteIndex <
limit,
- Let value be
GetValueFromBuffer (srcBuffer, srcByteIndex, srcType,true ,unordered ). - Perform
SetValueInBuffer (targetBuffer, targetByteIndex, targetType, value,true ,unordered ). - Set srcByteIndex to srcByteIndex + srcElementSize.
- Set targetByteIndex to targetByteIndex + targetElementSize.
- Let value be
- Repeat, while targetByteIndex <
limit,
- Return
unused .
23.2.3.26.2 SetTypedArrayFromArrayLike ( target, targetOffset, source )
The abstract operation SetTypedArrayFromArrayLike takes arguments target (a
- Let targetRecord be
MakeTypedArrayWithBufferWitnessRecord (target,seq-cst ). - If
IsTypedArrayOutOfBounds (targetRecord) istrue , throw aTypeError exception. - Let targetLength be
TypedArrayLength (targetRecord). - Let src be ?
ToObject (source). - Let srcLength be ?
LengthOfArrayLike (src). - If targetOffset = +∞, throw a
RangeError exception. - If srcLength + targetOffset >
targetLength, throw a
RangeError exception. - Let k be 0.
- Repeat, while k < srcLength,
- Let Pk be !
ToString (𝔽 (k)). - Let value be ?
Get (src, Pk). - Let targetIndex be
𝔽 (targetOffset + k). - Perform ?
TypedArraySetElement (target, targetIndex, value). - Set k to k + 1.
- Let Pk be !
- Return
unused .
23.2.3.27 %TypedArray%.prototype.slice ( start, end )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.slice as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let srcArrayLength be
TypedArrayLength (taRecord). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let startIndex be 0.
- Else if relativeStart < 0, let
startIndex be
max (srcArrayLength + relativeStart, 0). - Else, let startIndex be
min (relativeStart, srcArrayLength). - If end is
undefined , let relativeEnd be srcArrayLength; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let endIndex be 0.
- Else if relativeEnd < 0, let
endIndex
be
max (srcArrayLength + relativeEnd, 0). - Else, let endIndex be
min (relativeEnd, srcArrayLength). - Let countBytes be
max (endIndex - startIndex, 0). - Let A be ?
TypedArraySpeciesCreate (O, «𝔽 (countBytes) »). - If countBytes > 0, then
- Set taRecord to
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Set endIndex to
min (endIndex,TypedArrayLength (taRecord)). - Set countBytes to
max (endIndex - startIndex, 0). - Let srcType be
TypedArrayElementType (O). - Let targetType be
TypedArrayElementType (A). - If srcType is targetType, then
- NOTE: The transfer must be performed in a manner that preserves the bit-level encoding of the source data.
- Let srcBuffer be O.[[ViewedArrayBuffer]].
- Let targetBuffer be A.[[ViewedArrayBuffer]].
- Let elementSize be
TypedArrayElementSize (O). - Let srcByteOffset be O.[[ByteOffset]].
- Let srcByteIndex be (startIndex × elementSize) + srcByteOffset.
- Let targetByteIndex be A.[[ByteOffset]].
- Let endByteIndex be targetByteIndex + (countBytes × elementSize).
- Repeat, while targetByteIndex <
endByteIndex,
- Let value be
GetValueFromBuffer (srcBuffer, srcByteIndex,uint8 ,true ,unordered ). - Perform
SetValueInBuffer (targetBuffer, targetByteIndex,uint8 , value,true ,unordered ). - Set srcByteIndex to srcByteIndex + 1.
- Set targetByteIndex to targetByteIndex + 1.
- Let value be
- Else,
- Set taRecord to
- Return A.
This method is not generic. The
23.2.3.28 %TypedArray%.prototype.some ( callbackfn [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.some as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Let k be 0.
- Repeat, while k < len,
- Return
false .
This method is not generic. The
23.2.3.29 %TypedArray%.prototype.sort ( comparefn )
This is a distinct method that, except as described below, implements the same requirements as those
of
Array.prototype.sort as defined in
This method is not generic. The
It performs the following steps when called:
- If comparefn is not
undefined andIsCallable (comparefn) isfalse , throw aTypeError exception. - Let obj be the
this value. - Let taRecord be ?
ValidateTypedArray (obj,seq-cst ). - Let len be
TypedArrayLength (taRecord). - NOTE: The following closure performs a numeric comparison
rather
than the string comparison used in
23.1.3.30 . - Let SortCompare be a new
Abstract Closure with parameters (x, y) that captures comparefn and performs the following steps when called:- Return ?
CompareTypedArrayElements (x, y, comparefn).
- Return ?
- Let sortedList be ?
SortIndexedProperties (obj, len, SortCompare,read-through-holes ). - Let j be 0.
- Repeat, while j < len,
- Return obj.
Because
23.2.3.30 %TypedArray%.prototype.subarray ( start, end )
This method returns a new TypedArray whose element type is the element type of this
TypedArray and whose ArrayBuffer is the ArrayBuffer of this TypedArray,
referencing
the elements in the
It performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[TypedArrayName]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let buffer be O.[[ViewedArrayBuffer]].
- Let srcRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (srcRecord) istrue , then- Let srcLength be 0.
- Else,
- Let srcLength be
TypedArrayLength (srcRecord).
- Let srcLength be
- Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let startIndex be 0.
- Else if relativeStart < 0, let
startIndex be
max (srcLength + relativeStart, 0). - Else, let startIndex be
min (relativeStart, srcLength). - Let elementSize be
TypedArrayElementSize (O). - Let srcByteOffset be O.[[ByteOffset]].
- Let beginByteOffset be srcByteOffset + (startIndex × elementSize).
- If O.[[ArrayLength]] is
auto and end isundefined , then- Let argumentsList be « buffer,
𝔽 (beginByteOffset) ».
- Let argumentsList be « buffer,
- Else,
- If end is
undefined , let relativeEnd be srcLength; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let endIndex be 0.
- Else if relativeEnd < 0, let
endIndex be
max (srcLength + relativeEnd, 0). - Else, let endIndex be
min (relativeEnd, srcLength). - Let newLength be
max (endIndex - startIndex, 0). - Let argumentsList be « buffer,
𝔽 (beginByteOffset),𝔽 (newLength) ».
- If end is
- Return ?
TypedArraySpeciesCreate (O, argumentsList).
This method is not generic. The
23.2.3.31 %TypedArray%.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
This is a distinct method that implements the same algorithm as
Array.prototype.toLocaleString as defined in
This method is not generic.
If the ECMAScript implementation includes the ECMA-402 Internationalization API this method is
based
upon the algorithm for Array.prototype.toLocaleString that is in the ECMA-402
specification.
23.2.3.32 %TypedArray%.prototype.toReversed ( )
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let length be
TypedArrayLength (taRecord). - Let A be ?
TypedArrayCreateSameType (O, «𝔽 (length) »). - Let k be 0.
- Repeat, while k < length,
- Return A.
23.2.3.33 %TypedArray%.prototype.toSorted ( comparefn )
This method performs the following steps when called:
- If comparefn is not
undefined andIsCallable (comparefn) isfalse , throw aTypeError exception. - Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let A be ?
TypedArrayCreateSameType (O, «𝔽 (len) »). - NOTE: The following closure performs a numeric comparison
rather
than the string comparison used in
23.1.3.34 . - Let SortCompare be a new
Abstract Closure with parameters (x, y) that captures comparefn and performs the following steps when called:- Return ?
CompareTypedArrayElements (x, y, comparefn).
- Return ?
- Let sortedList be ?
SortIndexedProperties (O, len, SortCompare,read-through-holes ). - Let j be 0.
- Repeat, while j < len,
- Return A.
23.2.3.34 %TypedArray%.prototype.toString ( )
The initial value of the
23.2.3.35 %TypedArray%.prototype.values ( )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
ValidateTypedArray (O,seq-cst ). - Return
CreateArrayIterator (O,value ).
23.2.3.36 %TypedArray%.prototype.with ( index, value )
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let relativeIndex be ?
ToIntegerOrInfinity (index). - If relativeIndex ≥ 0, let actualIndex be relativeIndex.
- Else, let actualIndex be len + relativeIndex.
- If O.[[ContentType]] is
bigint , let numericValue be ?ToBigInt (value). - Else, let numericValue be ?
ToNumber (value). - If
IsValidIntegerIndex (O,𝔽 (actualIndex)) isfalse , throw aRangeError exception. - Let A be ?
TypedArrayCreateSameType (O, «𝔽 (len) »). - Let k be 0.
- Repeat, while k < len,
- Return A.
23.2.3.37 %TypedArray%.prototype [ @@iterator ] ( )
The initial value of the
23.2.3.38 get %TypedArray%.prototype [ @@toStringTag ]
.prototype[@@toStringTag]
is an
- Let O be the
this value. - If O
is not an Object , returnundefined . - If O does not have a [[TypedArrayName]] internal slot, return
undefined . - Let name be O.[[TypedArrayName]].
Assert : nameis a String .- Return name.
This property has the attributes { [[Enumerable]]:
The initial value of the
23.2.4 Abstract Operations for TypedArray Objects
23.2.4.1 TypedArraySpeciesCreate ( exemplar, argumentList )
The abstract operation TypedArraySpeciesCreate takes arguments exemplar (a
- Let defaultConstructor be the intrinsic object
associated with the
constructor name exemplar.[[TypedArrayName]] inTable 71 . - Let constructor be ?
SpeciesConstructor (exemplar, defaultConstructor). - Let result be ?
TypedArrayCreateFromConstructor (constructor, argumentList). Assert : result has [[TypedArrayName]] and [[ContentType]] internal slots.- If result.[[ContentType]]
is
not exemplar.[[ContentType]], throw a
TypeError exception. - Return result.
23.2.4.2 TypedArrayCreateFromConstructor ( constructor, argumentList )
The abstract operation TypedArrayCreateFromConstructor takes arguments constructor (a
- Let newTypedArray be ?
Construct (constructor, argumentList). - Let taRecord be ?
ValidateTypedArray (newTypedArray,seq-cst ). - If the number of elements in argumentList is 1 and
argumentList[0]
is a Number , then- If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Let length be
TypedArrayLength (taRecord). - If length <
ℝ (argumentList[0]), throw aTypeError exception.
- If
- Return newTypedArray.
23.2.4.3 TypedArrayCreateSameType ( exemplar, argumentList )
The abstract operation TypedArrayCreateSameType takes arguments exemplar (a
- Let constructor be the intrinsic object associated
with the
constructor name exemplar.[[TypedArrayName]] inTable 71 . - Let result be ?
TypedArrayCreateFromConstructor (constructor, argumentList). Assert : result has [[TypedArrayName]] and [[ContentType]] internal slots.Assert : result.[[ContentType]] is exemplar.[[ContentType]].- Return result.
23.2.4.4 ValidateTypedArray ( O, order )
The abstract operation ValidateTypedArray takes arguments O (an
- Perform ?
RequireInternalSlot (O, [[TypedArrayName]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (O, order). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Return taRecord.
23.2.4.5 TypedArrayElementSize ( O )
The abstract operation TypedArrayElementSize takes argument O (a
- Return the Element Size value specified in
Table 71 for O.[[TypedArrayName]].
23.2.4.6 TypedArrayElementType ( O )
The abstract operation TypedArrayElementType takes argument O (a
- Return the Element Type value specified in
Table 71 for O.[[TypedArrayName]].
23.2.4.7 CompareTypedArrayElements ( x, y, comparefn )
The abstract operation CompareTypedArrayElements takes arguments x (a Number or a BigInt),
y (a Number or a BigInt), and comparefn (a
Assert : xis a Number and yis a Number , or xis a BigInt and yis a BigInt .- If comparefn is not
undefined , then - If x and y are both
NaN , return+0 𝔽. - If x is
NaN , return1 𝔽. - If y is
NaN , return-1 𝔽. - If x < y, return
-1 𝔽. - If x > y, return
1 𝔽. - If x is
-0 𝔽 and y is+0 𝔽, return-1 𝔽. - If x is
+0 𝔽 and y is-0 𝔽, return1 𝔽. - Return
+0 𝔽.
23.2.5 The TypedArray Constructors
Each TypedArray
- is an intrinsic object that has the structure described below, differing only in the name used as
the
constructor name instead of TypedArray, inTable 71 . - is a function whose behaviour differs based upon the number and types of its arguments. The actual behaviour of a call of TypedArray depends upon the number and kind of arguments that are passed to it.
- is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified TypedArray behaviour must include asupercall to the TypedArrayconstructor to create and initialize the subclass instance with the internal state necessary to support the%TypedArray% .prototypebuilt-in methods.
23.2.5.1 TypedArray ( ...args )
Each TypedArray
- If NewTarget is
undefined , throw aTypeError exception. - Let constructorName be the String value of the
Constructor Name value specified inTable 71 for this TypedArrayconstructor . - Let proto be
"%TypedArray.prototype%". - Let numberOfArgs be the number of elements in args.
- If numberOfArgs = 0, then
- Return ?
AllocateTypedArray (constructorName, NewTarget, proto, 0).
- Return ?
- Else,
- Let firstArgument be args[0].
- If firstArgument
is an Object , then- Let O be ?
AllocateTypedArray (constructorName, NewTarget, proto). - If firstArgument has a [[TypedArrayName]] internal slot, then
- Perform ?
InitializeTypedArrayFromTypedArray (O, firstArgument).
- Perform ?
- Else if firstArgument has an [[ArrayBufferData]] internal slot, then
- If numberOfArgs > 1, let
byteOffset be args[1]; else let byteOffset be
undefined . - If numberOfArgs > 2, let
length be args[2]; else let length be
undefined . - Perform ?
InitializeTypedArrayFromArrayBuffer (O, firstArgument, byteOffset, length).
- If numberOfArgs > 1, let
byteOffset be args[1]; else let byteOffset be
- Else,
Assert : firstArgumentis an Object and firstArgument does not have either a [[TypedArrayName]] or an [[ArrayBufferData]] internal slot.- Let usingIterator be ?
GetMethod (firstArgument,@@iterator ). - If usingIterator is not
undefined , then- Let values be ?
IteratorToList (?GetIteratorFromMethod (firstArgument, usingIterator)). - Perform ?
InitializeTypedArrayFromList (O, values).
- Let values be ?
- Else,
- NOTE: firstArgument is not an
Iterable
so assume it is already an
array-like object . - Perform ?
InitializeTypedArrayFromArrayLike (O, firstArgument).
- NOTE: firstArgument is not an
Iterable
so assume it is already an
- Return O.
- Let O be ?
- Else,
Assert : firstArgumentis not an Object .- Let elementLength be ?
ToIndex (firstArgument). - Return ?
AllocateTypedArray (constructorName, NewTarget, proto, elementLength).
23.2.5.1.1 AllocateTypedArray ( constructorName, newTarget, defaultProto [ , length ] )
The abstract operation AllocateTypedArray takes arguments constructorName (a String
which
is
the name of a
- Let proto be ?
GetPrototypeFromConstructor (newTarget, defaultProto). - Let obj be
TypedArrayCreate (proto). Assert : obj.[[ViewedArrayBuffer]] isundefined .- Set obj.[[TypedArrayName]] to constructorName.
- If constructorName is either
"BigInt64Array" or"BigUint64Array" , set obj.[[ContentType]] tobigint . - Otherwise, set obj.[[ContentType]] to
number . - If length is not present, then
- Set obj.[[ByteLength]] to 0.
- Set obj.[[ByteOffset]] to 0.
- Set obj.[[ArrayLength]] to 0.
- Else,
- Perform ?
AllocateTypedArrayBuffer (obj, length).
- Perform ?
- Return obj.
23.2.5.1.2 InitializeTypedArrayFromTypedArray ( O, srcArray )
The abstract operation InitializeTypedArrayFromTypedArray takes arguments O (a
- Let srcData be srcArray.[[ViewedArrayBuffer]].
- Let elementType be
TypedArrayElementType (O). - Let elementSize be
TypedArrayElementSize (O). - Let srcType be
TypedArrayElementType (srcArray). - Let srcElementSize be
TypedArrayElementSize (srcArray). - Let srcByteOffset be srcArray.[[ByteOffset]].
- Let srcRecord be
MakeTypedArrayWithBufferWitnessRecord (srcArray,seq-cst ). - If
IsTypedArrayOutOfBounds (srcRecord) istrue , throw aTypeError exception. - Let elementLength be
TypedArrayLength (srcRecord). - Let byteLength be elementSize × elementLength.
- If elementType is srcType, then
- Let data be ?
CloneArrayBuffer (srcData, srcByteOffset, byteLength).
- Let data be ?
- Else,
- Let data be ?
AllocateArrayBuffer (%ArrayBuffer% , byteLength). - If srcArray.[[ContentType]] is not O.[[ContentType]], throw a
TypeError exception. - Let srcByteIndex be srcByteOffset.
- Let targetByteIndex be 0.
- Let count be elementLength.
- Repeat, while count > 0,
- Let value be
GetValueFromBuffer (srcData, srcByteIndex, srcType,true ,unordered ). - Perform
SetValueInBuffer (data, targetByteIndex, elementType, value,true ,unordered ). - Set srcByteIndex to srcByteIndex + srcElementSize.
- Set targetByteIndex to targetByteIndex + elementSize.
- Set count to count - 1.
- Let value be
- Let data be ?
- Set O.[[ViewedArrayBuffer]] to data.
- Set O.[[ByteLength]] to byteLength.
- Set O.[[ByteOffset]] to 0.
- Set O.[[ArrayLength]] to elementLength.
- Return
unused .
23.2.5.1.3 InitializeTypedArrayFromArrayBuffer ( O, buffer, byteOffset, length )
The abstract operation InitializeTypedArrayFromArrayBuffer takes arguments O (a
- Let elementSize be
TypedArrayElementSize (O). - Let offset be ?
ToIndex (byteOffset). - If offset
modulo elementSize ≠ 0, throw aRangeError exception. - Let bufferIsFixedLength be
IsFixedLengthArrayBuffer (buffer). - If length is not
undefined , then- Let newLength be ?
ToIndex (length).
- Let newLength be ?
- If
IsDetachedBuffer (buffer) istrue , throw aTypeError exception. - Let bufferByteLength be
ArrayBufferByteLength (buffer,seq-cst ). - If length is
undefined and bufferIsFixedLength isfalse , then- If offset > bufferByteLength,
throw a
RangeError exception. - Set O.[[ByteLength]]
to
auto . - Set O.[[ArrayLength]]
to
auto .
- If offset > bufferByteLength,
throw a
- Else,
- If length is
undefined , then- If bufferByteLength
modulo elementSize ≠ 0, throw aRangeError exception. - Let newByteLength be bufferByteLength - offset.
- If newByteLength < 0, throw a
RangeError exception.
- If bufferByteLength
- Else,
- Let newByteLength be newLength × elementSize.
- If offset + newByteLength
>
bufferByteLength, throw a
RangeError exception.
- Set O.[[ByteLength]] to newByteLength.
- Set O.[[ArrayLength]] to newByteLength / elementSize.
- If length is
- Set O.[[ViewedArrayBuffer]] to buffer.
- Set O.[[ByteOffset]] to offset.
- Return
unused .
23.2.5.1.4 InitializeTypedArrayFromList ( O, values )
The abstract operation InitializeTypedArrayFromList takes arguments O (a
- Let len be the number of elements in values.
- Perform ?
AllocateTypedArrayBuffer (O, len). - Let k be 0.
- Repeat, while k < len,
Assert : values is now an emptyList .- Return
unused .
23.2.5.1.5 InitializeTypedArrayFromArrayLike ( O, arrayLike )
The abstract operation InitializeTypedArrayFromArrayLike takes arguments O (a
- Let len be ?
LengthOfArrayLike (arrayLike). - Perform ?
AllocateTypedArrayBuffer (O, len). - Let k be 0.
- Repeat, while k < len,
- Return
unused .
23.2.5.1.6 AllocateTypedArrayBuffer ( O, length )
The abstract operation AllocateTypedArrayBuffer takes arguments O (a
Assert : O.[[ViewedArrayBuffer]] isundefined .- Let elementSize be
TypedArrayElementSize (O). - Let byteLength be elementSize × length.
- Let data be ?
AllocateArrayBuffer (%ArrayBuffer% , byteLength). - Set O.[[ViewedArrayBuffer]] to data.
- Set O.[[ByteLength]] to byteLength.
- Set O.[[ByteOffset]] to 0.
- Set O.[[ArrayLength]] to length.
- Return
unused .
23.2.6 Properties of the TypedArray Constructors
Each TypedArray
- has a [[Prototype]] internal slot whose value is
%TypedArray% . - has a
"length" property whose value is3 𝔽. - has a
"name" property whose value is the String value of theconstructor name specified for it inTable 71 . - has the following properties:
23.2.6.1 TypedArray.BYTES_PER_ELEMENT
The value of TypedArray.BYTES_PER_ELEMENT is the Element Size value specified
in
This property has the attributes { [[Writable]]:
23.2.6.2 TypedArray.prototype
The initial value of TypedArray.prototype is the corresponding
TypedArray prototype intrinsic object (
This property has the attributes { [[Writable]]:
23.2.7 Properties of the TypedArray Prototype Objects
Each TypedArray prototype object:
- has a [[Prototype]] internal slot whose value is
%TypedArray.prototype% . - is an
ordinary object . - does not have a [[ViewedArrayBuffer]] or any other of the internal slots that are specific to TypedArray instance objects.
23.2.7.1 TypedArray.prototype.BYTES_PER_ELEMENT
The value of TypedArray.prototype.BYTES_PER_ELEMENT is the Element Size value
specified in
This property has the attributes { [[Writable]]:
23.2.7.2 TypedArray.prototype.constructor
The initial value of the
23.2.8 Properties of TypedArray Instances
TypedArray instances are
24 Keyed Collections
24.1 Map Objects
Maps are collections of key/value pairs where both the keys and values may be arbitrary
Maps must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structure used in this specification is only intended to describe the required observable semantics of Maps. It is not intended to be a viable implementation model.
24.1.1 The Map Constructor
The Map
- is %Map%.
- is the initial value of the
"Map" property of theglobal object . - creates and initializes a new Map when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Map behaviour must include asupercall to the Mapconstructor to create and initialize the subclass instance with the internal state necessary to support theMap.prototypebuilt-in methods.
24.1.1.1 Map ( [ iterable ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Let map be ?
OrdinaryCreateFromConstructor (NewTarget,"%Map.prototype%" , « [[MapData]] »). - Set map.[[MapData]] to a
new
empty
List . - If iterable is either
undefined ornull , return map. - Let adder be ?
Get (map,"set" ). - If
IsCallable (adder) isfalse , throw aTypeError exception. - Return ?
AddEntriesFromIterable (map, iterable, adder).
If the parameter iterable is present, it is expected to be an object that implements
an
24.1.1.2 AddEntriesFromIterable ( target, iterable, adder )
The abstract operation AddEntriesFromIterable takes arguments target (an Object),
iterable (an
- Let iteratorRecord be ?
GetIterator (iterable,sync ). - Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , return target. - If next
is not an Object , then- Let error be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iteratorRecord, error).
- Let error be
- Let k be
Completion (Get (next,"0" )). IfAbruptCloseIterator (k, iteratorRecord).- Let v be
Completion (Get (next,"1" )). IfAbruptCloseIterator (v, iteratorRecord).- Let status be
Completion (Call (adder, target, « k, v »)). IfAbruptCloseIterator (status, iteratorRecord).
- Let next be ?
The parameter iterable is expected to be an object that implements an
24.1.2 Properties of the Map Constructor
The Map
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
24.1.2.1 Map.groupBy ( items, callbackfn )
callbackfn should be a function that accepts two arguments. groupBy calls
callbackfn once for each element in items, in ascending order, and
constructs
a
new Map. Each value returned by callbackfn is used as a key in the Map. For each such
key,
the result Map has an entry whose key is that key and whose value is an array containing all the
elements for which callbackfn returned that key.
callbackfn is called with two arguments: the value of the element and the index of the element.
The return value of groupBy is a Map.
This function performs the following steps when called:
- Let groups be ?
GroupBy (items, callbackfn,zero ). - Let map be !
Construct (%Map% ). - For each
Record { [[Key]], [[Elements]] } g of groups, do- Let elements be
CreateArrayFromList (g.[[Elements]]). - Let entry be the
Record { [[Key]]: g.[[Key]], [[Value]]: elements }. - Append entry to map.[[MapData]].
- Let elements be
- Return map.
24.1.2.2 Map.prototype
The initial value of Map.prototype is the
This property has the attributes { [[Writable]]:
24.1.2.3 get Map [ @@species ]
Map[@@species] is an
- Return the
this value.
The value of the
Methods that create derived collection objects should call
24.1.3 Properties of the Map Prototype Object
The Map prototype object:
- is %Map.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[MapData]] internal slot.
24.1.3.1 Map.prototype.clear ( )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - For each
Record { [[Key]], [[Value]] } p of M.[[MapData]], do- Set p.[[Key]] to
empty . - Set p.[[Value]] to
empty .
- Set p.[[Key]] to
- Return
undefined .
24.1.3.2 Map.prototype.constructor
The initial value of Map.prototype.constructor is
24.1.3.3 Map.prototype.delete ( key )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - For each
Record { [[Key]], [[Value]] } p of M.[[MapData]], do- If p.[[Key]] is not
empty andSameValueZero (p.[[Key]], key) istrue , then- Set p.[[Key]] to
empty . - Set p.[[Value]]
to
empty . - Return
true .
- Set p.[[Key]] to
- If p.[[Key]] is not
- Return
false .
The value
24.1.3.4 Map.prototype.entries ( )
This method performs the following steps when called:
- Let M be the
this value. - Return ?
CreateMapIterator (M,key+value ).
24.1.3.5 Map.prototype.forEach ( callbackfn [ , thisArg ] )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Let entries be M.[[MapData]].
- Let numEntries be the number of elements in entries.
- Let index be 0.
- Repeat, while index < numEntries,
- Let e be entries[index].
- Set index to index + 1.
- If e.[[Key]] is not
empty , then- Perform ?
Call (callbackfn, thisArg, « e.[[Value]], e.[[Key]], M »). - NOTE: The number of elements in entries may have increased during execution of callbackfn.
- Set numEntries to the number of elements in entries.
- Perform ?
- Return
undefined .
callbackfn should be a function that accepts three arguments. forEach
calls
callbackfn once for each key/value pair present in the Map, in key insertion order.
callbackfn is called only for keys of the Map which actually exist; it is not called
for
keys that have been deleted from the Map.
If a thisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the value of the item, the key of the item, and the Map being traversed.
forEach does not directly mutate the object on which it is called but the object may
be
mutated by the calls to callbackfn. Each entry of a map's [[MapData]] is only visited once. New keys added after the call to
forEach begins are visited. A key will be revisited if it is deleted after it has
been
visited and then re-added before the forEach call completes. Keys that are deleted
after
the call to forEach begins and before being visited are not visited unless the key is
added again before the forEach call completes.
24.1.3.6 Map.prototype.get ( key )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - For each
Record { [[Key]], [[Value]] } p of M.[[MapData]], do- If p.[[Key]] is not
empty andSameValueZero (p.[[Key]], key) istrue , return p.[[Value]].
- If p.[[Key]] is not
- Return
undefined .
24.1.3.7 Map.prototype.has ( key )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - For each
Record { [[Key]], [[Value]] } p of M.[[MapData]], do- If p.[[Key]] is not
empty andSameValueZero (p.[[Key]], key) istrue , returntrue .
- If p.[[Key]] is not
- Return
false .
24.1.3.8 Map.prototype.keys ( )
This method performs the following steps when called:
- Let M be the
this value. - Return ?
CreateMapIterator (M,key ).
24.1.3.9 Map.prototype.set ( key, value )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - For each
Record { [[Key]], [[Value]] } p of M.[[MapData]], do- If p.[[Key]] is not
empty andSameValueZero (p.[[Key]], key) istrue , then- Set p.[[Value]] to value.
- Return M.
- If p.[[Key]] is not
- If key is
-0 𝔽, set key to+0 𝔽. - Let p be the
Record { [[Key]]: key, [[Value]]: value }. - Append p to M.[[MapData]].
- Return M.
24.1.3.10 get Map.prototype.size
Map.prototype.size is an
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - Let count be 0.
- For each
Record { [[Key]], [[Value]] } p of M.[[MapData]], do- If p.[[Key]] is not
empty , set count to count + 1.
- If p.[[Key]] is not
- Return
𝔽 (count).
24.1.3.11 Map.prototype.values ( )
This method performs the following steps when called:
- Let M be the
this value. - Return ?
CreateMapIterator (M,value ).
24.1.3.12 Map.prototype [ @@iterator ] ( )
The initial value of the
24.1.3.13 Map.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
24.1.4 Properties of Map Instances
Map instances are
24.1.5 Map Iterator Objects
A Map Iterator is an object, that represents a specific iteration over some specific Map instance
object.
There is not a named
24.1.5.1 CreateMapIterator ( map, kind )
The abstract operation CreateMapIterator takes arguments map (an
- Perform ?
RequireInternalSlot (map, [[MapData]]). - Let closure be a new
Abstract Closure with no parameters that captures map and kind and performs the following steps when called:- Let entries be map.[[MapData]].
- Let index be 0.
- Let numEntries be the number of elements in entries.
- Repeat, while index <
numEntries,
- Let e be entries[index].
- Set index to index + 1.
- If e.[[Key]] is
not
empty , then- If kind is
key , then- Let result be e.[[Key]].
- Else if kind is
value , then- Let result be e.[[Value]].
- Else,
Assert : kind iskey+value .- Let result be
CreateArrayFromList (« e.[[Key]], e.[[Value]] »).
- Perform ?
GeneratorYield (CreateIterResultObject (result,false )). - NOTE: The number of elements in
entries
may have increased while execution of this abstract operation was paused by
Yield . - Set numEntries to the number of elements in entries.
- If kind is
- Return
undefined .
- Return
CreateIteratorFromClosure (closure,"%MapIteratorPrototype%" ,%MapIteratorPrototype% ).
24.1.5.2 The %MapIteratorPrototype% Object
The %MapIteratorPrototype% object:
- has properties that are inherited by all Map Iterator Objects.
- is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%IteratorPrototype% . - has the following properties:
24.1.5.2.1 %MapIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%MapIteratorPrototype%" ).
24.1.5.2.2 %MapIteratorPrototype% [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
24.2 Set Objects
Set objects are collections of
Set objects must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structure used in this specification is only intended to describe the required observable semantics of Set objects. It is not intended to be a viable implementation model.
24.2.1 The Set Constructor
The Set
- is %Set%.
- is the initial value of the
"Set" property of theglobal object . - creates and initializes a new Set object when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Set behaviour must include asupercall to the Setconstructor to create and initialize the subclass instance with the internal state necessary to support theSet.prototypebuilt-in methods.
24.2.1.1 Set ( [ iterable ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Let set be ?
OrdinaryCreateFromConstructor (NewTarget,"%Set.prototype%" , « [[SetData]] »). - Set set.[[SetData]] to a
new
empty
List . - If iterable is either
undefined ornull , return set. - Let adder be ?
Get (set,"add" ). - If
IsCallable (adder) isfalse , throw aTypeError exception. - Let iteratorRecord be ?
GetIterator (iterable,sync ). - Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , return set. - Let status be
Completion (Call (adder, set, « next »)). IfAbruptCloseIterator (status, iteratorRecord).
- Let next be ?
24.2.2 Properties of the Set Constructor
The Set
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
24.2.2.1 Set.prototype
The initial value of Set.prototype is the
This property has the attributes { [[Writable]]:
24.2.2.2 get Set [ @@species ]
Set[@@species] is an
- Return the
this value.
The value of the
Methods that create derived collection objects should call
24.2.3 Properties of the Set Prototype Object
The Set prototype object:
- is %Set.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[SetData]] internal slot.
24.2.3.1 Set.prototype.add ( value )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[SetData]]). - For each element e of S.[[SetData]], do
- If e is not
empty andSameValueZero (e, value) istrue , then- Return S.
- If e is not
- If value is
-0 𝔽, set value to+0 𝔽. - Append value to S.[[SetData]].
- Return S.
24.2.3.2 Set.prototype.clear ( )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[SetData]]). - For each element e of S.[[SetData]], do
- Replace the element of S.[[SetData]] whose value is e with an element whose value is
empty .
- Replace the element of S.[[SetData]] whose value is e with an element whose value is
- Return
undefined .
24.2.3.3 Set.prototype.constructor
The initial value of Set.prototype.constructor is
24.2.3.4 Set.prototype.delete ( value )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[SetData]]). - For each element e of S.[[SetData]], do
- If e is not
empty andSameValueZero (e, value) istrue , then- Replace the element of S.[[SetData]] whose value is e with an element whose value
is
empty . - Return
true .
- Replace the element of S.[[SetData]] whose value is e with an element whose value
is
- If e is not
- Return
false .
The value
24.2.3.5 Set.prototype.entries ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateSetIterator (S,key+value ).
For iteration purposes, a Set appears similar to a Map where each entry has the same value for its key and value.
24.2.3.6 Set.prototype.forEach ( callbackfn [ , thisArg ] )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[SetData]]). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Let entries be S.[[SetData]].
- Let numEntries be the number of elements in entries.
- Let index be 0.
- Repeat, while index < numEntries,
- Let e be entries[index].
- Set index to index + 1.
- If e is not
empty , then- Perform ?
Call (callbackfn, thisArg, « e, e, S »). - NOTE: The number of elements in entries may have increased during execution of callbackfn.
- Set numEntries to the number of elements in entries.
- Perform ?
- Return
undefined .
callbackfn should be a function that accepts three arguments. forEach
calls
callbackfn once for each value present in the Set object, in value insertion order.
callbackfn is called only for values of the Set which actually exist; it is not called
for
keys that have been deleted from the set.
If a thisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the first two arguments are a value contained in the Set. The same value is passed for both arguments. The Set object being traversed is passed as the third argument.
The callbackfn is called with three arguments to be consistent with the call back
functions used by forEach methods for Map and Array. For Sets, each item value is
considered to be both the key and the value.
forEach does not directly mutate the object on which it is called but the object may
be
mutated by the calls to callbackfn.
Each value is normally visited only once. However, a value will be revisited if it is deleted
after
it has been visited and then re-added before the forEach call completes. Values that
are
deleted after the call to forEach begins and before being visited are not visited
unless
the value is added again before the forEach call completes. New values added after
the
call to forEach begins are visited.
24.2.3.7 Set.prototype.has ( value )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[SetData]]). - For each element e of S.[[SetData]], do
- If e is not
empty andSameValueZero (e, value) istrue , returntrue .
- If e is not
- Return
false .
24.2.3.8 Set.prototype.keys ( )
The initial value of the
For iteration purposes, a Set appears similar to a Map where each entry has the same value for its key and value.
24.2.3.9 get Set.prototype.size
Set.prototype.size is an
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[SetData]]). - Let count be 0.
- For each element e of S.[[SetData]], do
- If e is not
empty , set count to count + 1.
- If e is not
- Return
𝔽 (count).
24.2.3.10 Set.prototype.values ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateSetIterator (S,value ).
24.2.3.11 Set.prototype [ @@iterator ] ( )
The initial value of the
24.2.3.12 Set.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
24.2.4 Properties of Set Instances
Set instances are
24.2.5 Set Iterator Objects
A Set Iterator is an
24.2.5.1 CreateSetIterator ( set, kind )
The abstract operation CreateSetIterator takes arguments set (an
- Perform ?
RequireInternalSlot (set, [[SetData]]). - Let closure be a new
Abstract Closure with no parameters that captures set and kind and performs the following steps when called:- Let index be 0.
- Let entries be set.[[SetData]].
- Let numEntries be the number of elements in entries.
- Repeat, while index <
numEntries,
- Let e be entries[index].
- Set index to index + 1.
- If e is not
empty , then- If kind is
key+value , then- Let result be
CreateArrayFromList (« e, e »). - Perform ?
GeneratorYield (CreateIterResultObject (result,false )).
- Let result be
- Else,
Assert : kind isvalue .- Perform ?
GeneratorYield (CreateIterResultObject (e,false )).
- NOTE: The number of elements in
entries
may have increased while execution of this abstract operation was paused by
Yield . - Set numEntries to the number of elements in entries.
- If kind is
- Return
undefined .
- Return
CreateIteratorFromClosure (closure,"%SetIteratorPrototype%" ,%SetIteratorPrototype% ).
24.2.5.2 The %SetIteratorPrototype% Object
The %SetIteratorPrototype% object:
- has properties that are inherited by all Set Iterator Objects.
- is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%IteratorPrototype% . - has the following properties:
24.2.5.2.1 %SetIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%SetIteratorPrototype%" ).
24.2.5.2.2 %SetIteratorPrototype% [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
24.3 WeakMap Objects
WeakMaps are collections of key/value pairs where the keys are objects and/or symbols and values may be
arbitrary
An implementation may impose an arbitrarily determined latency between the time a key/value pair of a WeakMap becomes inaccessible and the time when the key/value pair is removed from the WeakMap. If this latency was observable to ECMAScript program, it would be a source of indeterminacy that could impact program execution. For that reason, an ECMAScript implementation must not provide any means to observe a key of a WeakMap that does not require the observer to present the observed key.
WeakMaps must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of key/value pairs in the collection. The data structure used in this specification is only intended to describe the required observable semantics of WeakMaps. It is not intended to be a viable implementation model.
WeakMap and WeakSet are intended to provide mechanisms for dynamically associating state with an object or symbol in a manner that does not “leak” memory resources if, in the absence of the WeakMap or WeakSet instance, the object or symbol otherwise became inaccessible and subject to resource reclamation by the implementation's garbage collection mechanisms. This characteristic can be achieved by using an inverted per-object/symbol mapping of WeakMap or WeakSet instances to keys. Alternatively, each WeakMap or WeakSet instance may internally store its key and value data, but this approach requires coordination between the WeakMap or WeakSet implementation and the garbage collector. The following references describe mechanism that may be useful to implementations of WeakMap and WeakSet:
Barry Hayes. 1997. Ephemerons: a new finalization mechanism. In Proceedings of the 12th ACM SIGPLAN conference on Object-oriented programming, systems, languages, and applications (OOPSLA '97), A. Michael Berman (Ed.). ACM, New York, NY, USA, 176-183, http://doi.acm.org/10.1145/263698.263733.
Alexandra Barros, Roberto Ierusalimschy, Eliminating Cycles in Weak Tables. Journal of Universal Computer Science - J.UCS, vol. 14, no. 21, pp. 3481-3497, 2008, http://www.jucs.org/jucs_14_21/eliminating_cycles_in_weak
24.3.1 The WeakMap Constructor
The WeakMap
- is %WeakMap%.
- is the initial value of the
"WeakMap" property of theglobal object . - creates and initializes a new WeakMap when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified WeakMap behaviour must include asupercall to the WeakMapconstructor to create and initialize the subclass instance with the internal state necessary to support theWeakMap.prototypebuilt-in methods.
24.3.1.1 WeakMap ( [ iterable ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Let map be ?
OrdinaryCreateFromConstructor (NewTarget,"%WeakMap.prototype%" , « [[WeakMapData]] »). - Set map.[[WeakMapData]]
to
a
new empty
List . - If iterable is either
undefined ornull , return map. - Let adder be ?
Get (map,"set" ). - If
IsCallable (adder) isfalse , throw aTypeError exception. - Return ?
AddEntriesFromIterable (map, iterable, adder).
If the parameter iterable is present, it is expected to be an object that implements
an
24.3.2 Properties of the WeakMap Constructor
The WeakMap
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
24.3.2.1 WeakMap.prototype
The initial value of WeakMap.prototype is the
This property has the attributes { [[Writable]]:
24.3.3 Properties of the WeakMap Prototype Object
The WeakMap prototype object:
- is %WeakMap.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[WeakMapData]] internal slot.
24.3.3.1 WeakMap.prototype.constructor
The initial value of WeakMap.prototype.constructor is
24.3.3.2 WeakMap.prototype.delete ( key )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[WeakMapData]]). - If
CanBeHeldWeakly (key) isfalse , returnfalse . - For each
Record { [[Key]], [[Value]] } p of M.[[WeakMapData]], do- If p.[[Key]] is not
empty andSameValue (p.[[Key]], key) istrue , then- Set p.[[Key]] to
empty . - Set p.[[Value]]
to
empty . - Return
true .
- Set p.[[Key]] to
- If p.[[Key]] is not
- Return
false .
The value
24.3.3.3 WeakMap.prototype.get ( key )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[WeakMapData]]). - If
CanBeHeldWeakly (key) isfalse , returnundefined . - For each
Record { [[Key]], [[Value]] } p of M.[[WeakMapData]], do- If p.[[Key]] is not
empty andSameValue (p.[[Key]], key) istrue , return p.[[Value]].
- If p.[[Key]] is not
- Return
undefined .
24.3.3.4 WeakMap.prototype.has ( key )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[WeakMapData]]). - If
CanBeHeldWeakly (key) isfalse , returnfalse . - For each
Record { [[Key]], [[Value]] } p of M.[[WeakMapData]], do- If p.[[Key]] is not
empty andSameValue (p.[[Key]], key) istrue , returntrue .
- If p.[[Key]] is not
- Return
false .
24.3.3.5 WeakMap.prototype.set ( key, value )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[WeakMapData]]). - If
CanBeHeldWeakly (key) isfalse , throw aTypeError exception. - For each
Record { [[Key]], [[Value]] } p of M.[[WeakMapData]], do- If p.[[Key]] is not
empty andSameValue (p.[[Key]], key) istrue , then- Set p.[[Value]] to value.
- Return M.
- If p.[[Key]] is not
- Let p be the
Record { [[Key]]: key, [[Value]]: value }. - Append p to M.[[WeakMapData]].
- Return M.
24.3.3.6 WeakMap.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
24.3.4 Properties of WeakMap Instances
WeakMap instances are
24.4 WeakSet Objects
WeakSets are collections of objects and/or symbols. A distinct object or symbol may only occur once as an
element of a WeakSet's collection. A WeakSet may be queried to see if it contains a specific value, but no
mechanism is provided for enumerating the values it holds. In certain conditions, values which are not
An implementation may impose an arbitrarily determined latency between the time a value contained in a WeakSet becomes inaccessible and the time when the value is removed from the WeakSet. If this latency was observable to ECMAScript program, it would be a source of indeterminacy that could impact program execution. For that reason, an ECMAScript implementation must not provide any means to determine if a WeakSet contains a particular value that does not require the observer to present the observed value.
WeakSets must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structure used in this specification is only intended to describe the required observable semantics of WeakSets. It is not intended to be a viable implementation model.
See the NOTE in
24.4.1 The WeakSet Constructor
The WeakSet
- is %WeakSet%.
- is the initial value of the
"WeakSet" property of theglobal object . - creates and initializes a new WeakSet when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified WeakSet behaviour must include asupercall to the WeakSetconstructor to create and initialize the subclass instance with the internal state necessary to support theWeakSet.prototypebuilt-in methods.
24.4.1.1 WeakSet ( [ iterable ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Let set be ?
OrdinaryCreateFromConstructor (NewTarget,"%WeakSet.prototype%" , « [[WeakSetData]] »). - Set set.[[WeakSetData]]
to
a
new empty
List . - If iterable is either
undefined ornull , return set. - Let adder be ?
Get (set,"add" ). - If
IsCallable (adder) isfalse , throw aTypeError exception. - Let iteratorRecord be ?
GetIterator (iterable,sync ). - Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , return set. - Let status be
Completion (Call (adder, set, « next »)). IfAbruptCloseIterator (status, iteratorRecord).
- Let next be ?
24.4.2 Properties of the WeakSet Constructor
The WeakSet
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
24.4.2.1 WeakSet.prototype
The initial value of WeakSet.prototype is the
This property has the attributes { [[Writable]]:
24.4.3 Properties of the WeakSet Prototype Object
The WeakSet prototype object:
- is %WeakSet.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[WeakSetData]] internal slot.
24.4.3.1 WeakSet.prototype.add ( value )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[WeakSetData]]). - If
CanBeHeldWeakly (value) isfalse , throw aTypeError exception. - For each element e of S.[[WeakSetData]], do
- If e is not
empty andSameValue (e, value) istrue , then- Return S.
- If e is not
- Append value to S.[[WeakSetData]].
- Return S.
24.4.3.2 WeakSet.prototype.constructor
The initial value of WeakSet.prototype.constructor is
24.4.3.3 WeakSet.prototype.delete ( value )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[WeakSetData]]). - If
CanBeHeldWeakly (value) isfalse , returnfalse . - For each element e of S.[[WeakSetData]], do
- If e is not
empty andSameValue (e, value) istrue , then- Replace the element of S.[[WeakSetData]] whose value is e with an element whose
value
is
empty . - Return
true .
- Replace the element of S.[[WeakSetData]] whose value is e with an element whose
value
is
- If e is not
- Return
false .
The value
24.4.3.4 WeakSet.prototype.has ( value )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[WeakSetData]]). - If
CanBeHeldWeakly (value) isfalse , returnfalse . - For each element e of S.[[WeakSetData]], do
- If e is not
empty andSameValue (e, value) istrue , returntrue .
- If e is not
- Return
false .
24.4.3.5 WeakSet.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
24.4.4 Properties of WeakSet Instances
WeakSet instances are
25 Structured Data
25.1 ArrayBuffer Objects
25.1.1 Notation
The descriptions below in this section,
A read-modify-write modification
function is a mathematical function that is notationally represented as an abstract closure that
takes two
- They perform all their algorithm steps atomically.
- Their individual algorithm steps are not observable.
To aid verifying that a read-modify-write modification function's algorithm steps constitute a pure, mathematical function, the following editorial conventions are recommended:
- They do not access, directly or transitively via invoked
abstract operations and abstract closures, any language or specification values except their parameters and captured values. - They do not return
Completion Records .
25.1.2 Fixed-length and Resizable ArrayBuffer Objects
A fixed-length ArrayBuffer is an ArrayBuffer whose byte length cannot change after creation.
A resizable ArrayBuffer is an ArrayBuffer whose byte length may change after
creation via calls to
The kind of ArrayBuffer object that is created depends on the arguments passed to
25.1.3 Abstract Operations For ArrayBuffer Objects
25.1.3.1 AllocateArrayBuffer ( constructor, byteLength [ , maxByteLength ] )
The abstract operation AllocateArrayBuffer takes arguments constructor (a
- Let slots be « [[ArrayBufferData]], [[ArrayBufferByteLength]], [[ArrayBufferDetachKey]] ».
- If maxByteLength is present and
maxByteLength is not
empty , let allocatingResizableBuffer betrue ; otherwise let allocatingResizableBuffer befalse . - If allocatingResizableBuffer is
true , then- If byteLength > maxByteLength,
throw
a
RangeError exception. - Append [[ArrayBufferMaxByteLength]] to slots.
- If byteLength > maxByteLength,
throw
a
- Let obj be ?
OrdinaryCreateFromConstructor (constructor,"%ArrayBuffer.prototype%" , slots). - Let block be ?
CreateByteDataBlock (byteLength). - Set obj.[[ArrayBufferData]] to block.
- Set obj.[[ArrayBufferByteLength]] to byteLength.
- If allocatingResizableBuffer is
true , then- If it is not possible to create a
Data Block block consisting of maxByteLength bytes, throw aRangeError exception. - NOTE: Resizable ArrayBuffers are designed to be implementable with in-place growth. Implementations may throw if, for example, virtual memory cannot be reserved up front.
- Set obj.[[ArrayBufferMaxByteLength]] to maxByteLength.
- If it is not possible to create a
- Return obj.
25.1.3.2 ArrayBufferByteLength ( arrayBuffer, order )
The abstract operation ArrayBufferByteLength takes arguments arrayBuffer (an ArrayBuffer
or
SharedArrayBuffer) and order (
- If
IsSharedArrayBuffer (arrayBuffer) istrue and arrayBuffer has an [[ArrayBufferByteLengthData]] internal slot, then- Let bufferByteLengthBlock be arrayBuffer.[[ArrayBufferByteLengthData]].
- Let rawLength be
GetRawBytesFromSharedBlock (bufferByteLengthBlock, 0,biguint64 ,true , order). - Let isLittleEndian be the value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Return
ℝ (RawBytesToNumeric (biguint64 , rawLength, isLittleEndian)).
Assert :IsDetachedBuffer (arrayBuffer) isfalse .- Return arrayBuffer.[[ArrayBufferByteLength]].
25.1.3.3 ArrayBufferCopyAndDetach ( arrayBuffer, newLength, preserveResizability )
The abstract operation ArrayBufferCopyAndDetach takes arguments arrayBuffer (an
- Perform ?
RequireInternalSlot (arrayBuffer, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (arrayBuffer) istrue , throw aTypeError exception. - If newLength is
undefined , then- Let newByteLength be arrayBuffer.[[ArrayBufferByteLength]].
- Else,
- Let newByteLength be ?
ToIndex (newLength).
- Let newByteLength be ?
- If
IsDetachedBuffer (arrayBuffer) istrue , throw aTypeError exception. - If preserveResizability is
preserve-resizability andIsFixedLengthArrayBuffer (arrayBuffer) isfalse , then- Let newMaxByteLength be arrayBuffer.[[ArrayBufferMaxByteLength]].
- Else,
- Let newMaxByteLength be
empty .
- Let newMaxByteLength be
- If arrayBuffer.[[ArrayBufferDetachKey]] is not
undefined , throw aTypeError exception. - Let newBuffer be ?
AllocateArrayBuffer (%ArrayBuffer% , newByteLength, newMaxByteLength). - Let copyLength be
min (newByteLength, arrayBuffer.[[ArrayBufferByteLength]]). - Let fromBlock be arrayBuffer.[[ArrayBufferData]].
- Let toBlock be newBuffer.[[ArrayBufferData]].
- Perform
CopyDataBlockBytes (toBlock, 0, fromBlock, 0, copyLength). - NOTE: Neither creation of the new
Data Block nor copying from the oldData Block are observable. Implementations may implement this method as a zero-copy move or arealloc. - Perform !
DetachArrayBuffer (arrayBuffer). - Return newBuffer.
25.1.3.4 IsDetachedBuffer ( arrayBuffer )
The abstract operation IsDetachedBuffer takes argument arrayBuffer (an ArrayBuffer or a SharedArrayBuffer) and returns a Boolean. It performs the following steps when called:
- If arrayBuffer.[[ArrayBufferData]] is
null , returntrue . - Return
false .
25.1.3.5 DetachArrayBuffer ( arrayBuffer [ , key ] )
The abstract operation DetachArrayBuffer takes argument arrayBuffer (an ArrayBuffer) and
optional argument key (anything) and returns either a
Assert :IsSharedArrayBuffer (arrayBuffer) isfalse .- If key is not present, set key to
undefined . - If arrayBuffer.[[ArrayBufferDetachKey]] is not key, throw a
TypeError exception. - Set arrayBuffer.[[ArrayBufferData]] to
null . - Set arrayBuffer.[[ArrayBufferByteLength]] to 0.
- Return
unused .
Detaching an ArrayBuffer instance disassociates the
25.1.3.6 CloneArrayBuffer ( srcBuffer, srcByteOffset, srcLength )
The abstract operation CloneArrayBuffer takes arguments srcBuffer (an ArrayBuffer or a
SharedArrayBuffer), srcByteOffset (a non-negative
Assert :IsDetachedBuffer (srcBuffer) isfalse .- Let targetBuffer be ?
AllocateArrayBuffer (%ArrayBuffer% , srcLength). - Let srcBlock be srcBuffer.[[ArrayBufferData]].
- Let targetBlock be targetBuffer.[[ArrayBufferData]].
- Perform
CopyDataBlockBytes (targetBlock, 0, srcBlock, srcByteOffset, srcLength). - Return targetBuffer.
25.1.3.7 GetArrayBufferMaxByteLengthOption ( options )
The abstract operation GetArrayBufferMaxByteLengthOption takes argument options (an
- If options
is not an Object , returnempty . - Let maxByteLength be ?
Get (options,"maxByteLength" ). - If maxByteLength is
undefined , returnempty . - Return ?
ToIndex (maxByteLength).
25.1.3.8 HostResizeArrayBuffer ( buffer, newByteLength )
The
The implementation of HostResizeArrayBuffer must conform to the following requirements:
- The abstract operation does not detach buffer.
- If the abstract operation completes normally with
handled , buffer.[[ArrayBufferByteLength]] is newByteLength.
The default implementation of HostResizeArrayBuffer is to return
25.1.3.9 IsFixedLengthArrayBuffer ( arrayBuffer )
The abstract operation IsFixedLengthArrayBuffer takes argument arrayBuffer (an ArrayBuffer or a SharedArrayBuffer) and returns a Boolean. It performs the following steps when called:
- If arrayBuffer has an [[ArrayBufferMaxByteLength]] internal slot, return
false . - Return
true .
25.1.3.10 IsUnsignedElementType ( type )
The abstract operation IsUnsignedElementType takes argument type (a
- If type is one of
uint8 ,uint8clamped ,uint16 ,uint32 , orbiguint64 , returntrue . - Return
false .
25.1.3.11 IsUnclampedIntegerElementType ( type )
The abstract operation IsUnclampedIntegerElementType takes argument type (a
- If type is one of
int8 ,uint8 ,int16 ,uint16 ,int32 , oruint32 , returntrue . - Return
false .
25.1.3.12 IsBigIntElementType ( type )
The abstract operation IsBigIntElementType takes argument type (a
- If type is either
biguint64 orbigint64 , returntrue . - Return
false .
25.1.3.13 IsNoTearConfiguration ( type, order )
The abstract operation IsNoTearConfiguration takes arguments type (a
- If
IsUnclampedIntegerElementType (type) istrue , returntrue . - If
IsBigIntElementType (type) istrue and order is neitherinit norunordered , returntrue . - Return
false .
25.1.3.14 RawBytesToNumeric ( type, rawBytes, isLittleEndian )
The abstract operation RawBytesToNumeric takes arguments type (a
- Let elementSize be the Element Size value
specified
in
Table 71 for Element Type type. - If isLittleEndian is
false , reverse the order of the elements of rawBytes. - If type is
float32 , then- Let value be the byte elements of
rawBytes concatenated and interpreted as a little-endian bit string encoding of an
IEEE 754-2019 binary32 value. - If value is an
IEEE 754-2019 binary32 NaN value, return theNaN Number value. - Return the Number value that corresponds to value.
- Let value be the byte elements of
rawBytes concatenated and interpreted as a little-endian bit string encoding of an
- If type is
float64 , then- Let value be the byte elements of
rawBytes concatenated and interpreted as a little-endian bit string encoding of an
IEEE 754-2019 binary64 value. - If value is an
IEEE 754-2019 binary64 NaN value, return theNaN Number value. - Return the Number value that corresponds to value.
- Let value be the byte elements of
rawBytes concatenated and interpreted as a little-endian bit string encoding of an
- If
IsUnsignedElementType (type) istrue , then- Let intValue be the byte elements of rawBytes concatenated and interpreted as a bit string encoding of an unsigned little-endian binary number.
- Else,
- Let intValue be the byte elements of rawBytes concatenated and interpreted as a bit string encoding of a binary little-endian two's complement number of bit length elementSize × 8.
- If
IsBigIntElementType (type) istrue , return the BigInt value that corresponds to intValue. - Otherwise, return the Number value that corresponds to intValue.
25.1.3.15 GetRawBytesFromSharedBlock ( block, byteIndex, type, isTypedArray, order )
The abstract operation GetRawBytesFromSharedBlock takes arguments block (a
- Let elementSize be the Element Size value
specified
in
Table 71 for Element Type type. - Let execution be the [[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - If isTypedArray is
true andIsNoTearConfiguration (type, order) istrue , let noTear betrue ; otherwise let noTear befalse . - Let rawValue be a
List of length elementSize whose elements are nondeterministically chosenbyte values . - NOTE: In implementations, rawValue is the result
of
a
non-atomic or atomic read instruction on the underlying hardware. The nondeterminism is a semantic
prescription of the
memory model to describe observable behaviour of hardware with weak consistency. - Let readEvent be
ReadSharedMemory { [[Order]]: order, [[NoTear]]: noTear, [[Block]]: block, [[ByteIndex]]: byteIndex, [[ElementSize]]: elementSize }. - Append readEvent to eventsRecord.[[EventList]].
- Append
Chosen Value Record { [[Event]]: readEvent, [[ChosenValue]]: rawValue } to execution.[[ChosenValues]]. - Return rawValue.
25.1.3.16 GetValueFromBuffer ( arrayBuffer, byteIndex, type, isTypedArray, order [ , isLittleEndian ] )
The abstract operation GetValueFromBuffer takes arguments arrayBuffer (an ArrayBuffer or
SharedArrayBuffer), byteIndex (a non-negative
Assert :IsDetachedBuffer (arrayBuffer) isfalse .Assert : There are sufficient bytes in arrayBuffer starting at byteIndex to represent a value of type.- Let block be arrayBuffer.[[ArrayBufferData]].
- Let elementSize be the Element Size value
specified
in
Table 71 for Element Type type. - If
IsSharedArrayBuffer (arrayBuffer) istrue , thenAssert : block is aShared Data Block .- Let rawValue be
GetRawBytesFromSharedBlock (block, byteIndex, type, isTypedArray, order).
- Else,
Assert : The number of elements in rawValue is elementSize.- If isLittleEndian is not present, set
isLittleEndian to the value of the [[LittleEndian]] field of
the
surrounding agent 'sAgent Record . - Return
RawBytesToNumeric (type, rawValue, isLittleEndian).
25.1.3.17 NumericToRawBytes ( type, value, isLittleEndian )
The abstract operation NumericToRawBytes takes arguments type (a
- If type is
float32 , then- Let rawBytes be a
List whose elements are the 4 bytes that are the result of converting value toIEEE 754-2019 binary32 format using roundTiesToEven mode. The bytes are arranged in little endian order. If value isNaN , rawBytes may be set to any implementation chosenIEEE 754-2019 binary32 format Not-a-Number encoding. An implementation must always choose the same encoding for each implementation distinguishableNaN value.
- Let rawBytes be a
- Else if type is
float64 , then- Let rawBytes be a
List whose elements are the 8 bytes that are theIEEE 754-2019 binary64 format encoding of value. The bytes are arranged in little endian order. If value isNaN , rawBytes may be set to any implementation chosenIEEE 754-2019 binary64 format Not-a-Number encoding. An implementation must always choose the same encoding for each implementation distinguishableNaN value.
- Let rawBytes be a
- Else,
- Let n be the Element Size value specified in
Table 71 for Element Type type. - Let convOp be the abstract operation named in
the
Conversion Operation column in
Table 71 for Element Type type. - Let intValue be
ℝ (convOp(value)). - If intValue ≥ 0, then
- Let rawBytes be a
List whose elements are the n-byte binary encoding of intValue. The bytes are ordered in little endian order.
- Let rawBytes be a
- Else,
- Let rawBytes be a
List whose elements are the n-byte binary two's complement encoding of intValue. The bytes are ordered in little endian order.
- Let rawBytes be a
- Let n be the Element Size value specified in
- If isLittleEndian is
false , reverse the order of the elements of rawBytes. - Return rawBytes.
25.1.3.18 SetValueInBuffer ( arrayBuffer, byteIndex, type, value, isTypedArray, order [ , isLittleEndian ] )
The abstract operation SetValueInBuffer takes arguments arrayBuffer (an ArrayBuffer or
SharedArrayBuffer), byteIndex (a non-negative
Assert :IsDetachedBuffer (arrayBuffer) isfalse .Assert : There are sufficient bytes in arrayBuffer starting at byteIndex to represent a value of type.Assert : valueis a BigInt ifIsBigIntElementType (type) istrue ; otherwise, valueis a Number .- Let block be arrayBuffer.[[ArrayBufferData]].
- Let elementSize be the Element Size value
specified
in
Table 71 for Element Type type. - If isLittleEndian is not present, set
isLittleEndian to the value of the [[LittleEndian]] field of
the
surrounding agent 'sAgent Record . - Let rawBytes be
NumericToRawBytes (type, value, isLittleEndian). - If
IsSharedArrayBuffer (arrayBuffer) istrue , then- Let execution be the [[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - If isTypedArray is
true andIsNoTearConfiguration (type, order) istrue , let noTear betrue ; otherwise let noTear befalse . - Append
WriteSharedMemory { [[Order]]: order, [[NoTear]]: noTear, [[Block]]: block, [[ByteIndex]]: byteIndex, [[ElementSize]]: elementSize, [[Payload]]: rawBytes } to eventsRecord.[[EventList]].
- Let execution be the [[CandidateExecution]] field of the
- Else,
- Store the individual bytes of rawBytes into block, starting at block[byteIndex].
- Return
unused .
25.1.3.19 GetModifySetValueInBuffer ( arrayBuffer, byteIndex, type, value, op )
The abstract operation GetModifySetValueInBuffer takes arguments arrayBuffer (an
ArrayBuffer
or a SharedArrayBuffer), byteIndex (a non-negative
Assert :IsDetachedBuffer (arrayBuffer) isfalse .Assert : There are sufficient bytes in arrayBuffer starting at byteIndex to represent a value of type.Assert : valueis a BigInt ifIsBigIntElementType (type) istrue ; otherwise, valueis a Number .- Let block be arrayBuffer.[[ArrayBufferData]].
- Let elementSize be the Element Size value
specified
in
Table 71 for Element Type type. - Let isLittleEndian be the value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Let rawBytes be
NumericToRawBytes (type, value, isLittleEndian). - If
IsSharedArrayBuffer (arrayBuffer) istrue , then- Let execution be the [[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - Let rawBytesRead be a
List of length elementSize whose elements are nondeterministically chosenbyte values . - NOTE: In implementations, rawBytesRead is the
result of a load-link, of a load-exclusive, or of an operand of a read-modify-write
instruction
on
the underlying hardware. The nondeterminism is a semantic prescription of the
memory model to describe observable behaviour of hardware with weak consistency. - Let rmwEvent be
ReadModifyWriteSharedMemory { [[Order]]:seq-cst , [[NoTear]]:true , [[Block]]: block, [[ByteIndex]]: byteIndex, [[ElementSize]]: elementSize, [[Payload]]: rawBytes, [[ModifyOp]]: op }. - Append rmwEvent to eventsRecord.[[EventList]].
- Append
Chosen Value Record { [[Event]]: rmwEvent, [[ChosenValue]]: rawBytesRead } to execution.[[ChosenValues]].
- Let execution be the [[CandidateExecution]] field of the
- Else,
- Let rawBytesRead be a
List of length elementSize whose elements are the sequence of elementSize bytes starting with block[byteIndex]. - Let rawBytesModified be op(rawBytesRead, rawBytes).
- Store the individual bytes of rawBytesModified into block, starting at block[byteIndex].
- Let rawBytesRead be a
- Return
RawBytesToNumeric (type, rawBytesRead, isLittleEndian).
25.1.4 The ArrayBuffer Constructor
The ArrayBuffer
- is %ArrayBuffer%.
- is the initial value of the
"ArrayBuffer" property of theglobal object . - creates and initializes a new ArrayBuffer when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified ArrayBuffer behaviour must include asupercall to the ArrayBufferconstructor to create and initialize subclass instances with the internal state necessary to support theArrayBuffer.prototypebuilt-in methods.
25.1.4.1 ArrayBuffer ( length [ , options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Let byteLength be ?
ToIndex (length). - Let requestedMaxByteLength be ?
GetArrayBufferMaxByteLengthOption (options). - Return ?
AllocateArrayBuffer (NewTarget, byteLength, requestedMaxByteLength).
25.1.5 Properties of the ArrayBuffer Constructor
The ArrayBuffer
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
25.1.5.1 ArrayBuffer.isView ( arg )
This function performs the following steps when called:
- If arg
is not an Object , returnfalse . - If arg has a [[ViewedArrayBuffer]] internal slot, return
true . - Return
false .
25.1.5.2 ArrayBuffer.prototype
The initial value of ArrayBuffer.prototype is the
This property has the attributes { [[Writable]]:
25.1.5.3 get ArrayBuffer [ @@species ]
ArrayBuffer[@@species] is an
- Return the
this value.
The value of the
25.1.6 Properties of the ArrayBuffer Prototype Object
The ArrayBuffer prototype object:
- is %ArrayBuffer.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have an [[ArrayBufferData]] or [[ArrayBufferByteLength]] internal slot.
25.1.6.1 get ArrayBuffer.prototype.byteLength
ArrayBuffer.prototype.byteLength is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - If
IsDetachedBuffer (O) istrue , return+0 𝔽. - Let length be O.[[ArrayBufferByteLength]].
- Return
𝔽 (length).
25.1.6.2 ArrayBuffer.prototype.constructor
The initial value of ArrayBuffer.prototype.constructor is
25.1.6.3 get ArrayBuffer.prototype.detached
ArrayBuffer.prototype.detached is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - Return
IsDetachedBuffer (O).
25.1.6.4 get ArrayBuffer.prototype.maxByteLength
ArrayBuffer.prototype.maxByteLength is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - If
IsDetachedBuffer (O) istrue , return+0 𝔽. - If
IsFixedLengthArrayBuffer (O) istrue , then- Let length be O.[[ArrayBufferByteLength]].
- Else,
- Let length be O.[[ArrayBufferMaxByteLength]].
- Return
𝔽 (length).
25.1.6.5 get ArrayBuffer.prototype.resizable
ArrayBuffer.prototype.resizable is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - If
IsFixedLengthArrayBuffer (O) isfalse , returntrue ; otherwise returnfalse .
25.1.6.6 ArrayBuffer.prototype.resize ( newLength )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferMaxByteLength]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - Let newByteLength be ?
ToIndex (newLength). - If
IsDetachedBuffer (O) istrue , throw aTypeError exception. - If newByteLength > O.[[ArrayBufferMaxByteLength]], throw a
RangeError exception. - Let hostHandled be ?
HostResizeArrayBuffer (O, newByteLength). - If hostHandled is
handled , returnundefined . - Let oldBlock be O.[[ArrayBufferData]].
- Let newBlock be ?
CreateByteDataBlock (newByteLength). - Let copyLength be
min (newByteLength, O.[[ArrayBufferByteLength]]). - Perform
CopyDataBlockBytes (newBlock, 0, oldBlock, 0, copyLength). - NOTE: Neither creation of the new
Data Block nor copying from the oldData Block are observable. Implementations may implement this method as in-place growth or shrinkage. - Set O.[[ArrayBufferData]] to newBlock.
- Set O.[[ArrayBufferByteLength]] to newByteLength.
- Return
undefined .
25.1.6.7 ArrayBuffer.prototype.slice ( start, end )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - If
IsDetachedBuffer (O) istrue , throw aTypeError exception. - Let len be O.[[ArrayBufferByteLength]].
- Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let first be 0.
- Else if relativeStart < 0, let first
be
max (len + relativeStart, 0). - Else, let first be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let final be 0.
- Else if relativeEnd < 0, let final
be
max (len + relativeEnd, 0). - Else, let final be
min (relativeEnd, len). - Let newLen be
max (final - first, 0). - Let ctor be ?
SpeciesConstructor (O,%ArrayBuffer% ). - Let new be ?
Construct (ctor, «𝔽 (newLen) »). - Perform ?
RequireInternalSlot (new, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (new) istrue , throw aTypeError exception. - If
IsDetachedBuffer (new) istrue , throw aTypeError exception. - If
SameValue (new, O) istrue , throw aTypeError exception. - If new.[[ArrayBufferByteLength]] < newLen, throw a
TypeError exception. - NOTE: Side-effects of the above steps may have detached or resized O.
- If
IsDetachedBuffer (O) istrue , throw aTypeError exception. - Let fromBuf be O.[[ArrayBufferData]].
- Let toBuf be new.[[ArrayBufferData]].
- Let currentLen be O.[[ArrayBufferByteLength]].
- If first < currentLen, then
- Let count be
min (newLen, currentLen - first). - Perform
CopyDataBlockBytes (toBuf, 0, fromBuf, first, count).
- Let count be
- Return new.
25.1.6.8 ArrayBuffer.prototype.transfer ( [ newLength ] )
This method performs the following steps when called:
- Let O be the
this value. - Return ?
ArrayBufferCopyAndDetach (O, newLength,preserve-resizability ).
25.1.6.9 ArrayBuffer.prototype.transferToFixedLength ( [ newLength ] )
This method performs the following steps when called:
- Let O be the
this value. - Return ?
ArrayBufferCopyAndDetach (O, newLength,fixed-length ).
25.1.6.10 ArrayBuffer.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
25.1.7 Properties of ArrayBuffer Instances
ArrayBuffer instances inherit properties from the
ArrayBuffer instances whose [[ArrayBufferData]] is
ArrayBuffer instances whose [[ArrayBufferDetachKey]] is set to a value other
than
25.1.8 Resizable ArrayBuffer Guidelines
The following are guidelines for ECMAScript programmers working with
We recommend that programs be tested in their deployment environments where possible. The amount of available physical memory differs greatly between hardware devices. Similarly, virtual memory subsystems also differ greatly between hardware devices as well as operating systems. An application that runs without out-of-memory errors on a 64-bit desktop web browser could run out of memory on a 32-bit mobile web browser.
When choosing a value for the
Please note that successfully constructing a
The following are guidelines for ECMAScript implementers implementing
If a
If a
25.2 SharedArrayBuffer Objects
25.2.1 Fixed-length and Growable SharedArrayBuffer Objects
A fixed-length SharedArrayBuffer is a SharedArrayBuffer whose byte length cannot change after creation.
A growable SharedArrayBuffer is a SharedArrayBuffer whose byte length may
increase
after creation via calls to
The kind of SharedArrayBuffer object that is created depends on the arguments passed to
25.2.2 Abstract Operations for SharedArrayBuffer Objects
25.2.2.1 AllocateSharedArrayBuffer ( constructor, byteLength [ , maxByteLength ] )
The abstract operation AllocateSharedArrayBuffer takes arguments constructor (a
- Let slots be « [[ArrayBufferData]] ».
- If maxByteLength is present and
maxByteLength is not
empty , let allocatingGrowableBuffer betrue ; otherwise let allocatingGrowableBuffer befalse . - If allocatingGrowableBuffer is
true , then- If byteLength > maxByteLength,
throw
a
RangeError exception. - Append [[ArrayBufferByteLengthData]] and [[ArrayBufferMaxByteLength]] to slots.
- If byteLength > maxByteLength,
throw
a
- Else,
- Append [[ArrayBufferByteLength]] to slots.
- Let obj be ?
OrdinaryCreateFromConstructor (constructor,"%SharedArrayBuffer.prototype%" , slots). - If allocatingGrowableBuffer is
true , let allocLength be maxByteLength; otherwise let allocLength be byteLength. - Let block be ?
CreateSharedByteDataBlock (allocLength). - Set obj.[[ArrayBufferData]] to block.
- If allocatingGrowableBuffer is
true , thenAssert : byteLength ≤ maxByteLength.- Let byteLengthBlock be ?
CreateSharedByteDataBlock (8). - Perform
SetValueInBuffer (byteLengthBlock, 0,biguint64 ,ℤ (byteLength),true ,seq-cst ). - Set obj.[[ArrayBufferByteLengthData]] to byteLengthBlock.
- Set obj.[[ArrayBufferMaxByteLength]] to maxByteLength.
- Else,
- Set obj.[[ArrayBufferByteLength]] to byteLength.
- Return obj.
25.2.2.2 IsSharedArrayBuffer ( obj )
The abstract operation IsSharedArrayBuffer takes argument obj (an ArrayBuffer or a SharedArrayBuffer) and returns a Boolean. It tests whether an object is an ArrayBuffer, a SharedArrayBuffer, or a subtype of either. It performs the following steps when called:
- Let bufferData be obj.[[ArrayBufferData]].
- If bufferData is
null , returnfalse . - If bufferData is a
Data Block , returnfalse . Assert : bufferData is aShared Data Block .- Return
true .
25.2.2.3 HostGrowSharedArrayBuffer ( buffer, newByteLength )
The
The implementation of HostGrowSharedArrayBuffer must conform to the following requirements:
- If the abstract operation does not complete normally with
unhandled , and newByteLength < the current byte length of the buffer or newByteLength > buffer.[[ArrayBufferMaxByteLength]], throw aRangeError exception. - Let isLittleEndian be the value of the [[LittleEndian]] field
of
the
surrounding agent 'sAgent Record . If the abstract operation completes normally withhandled , aWriteSharedMemory orReadModifyWriteSharedMemory event whose [[Order]] isseq-cst , [[Payload]] isNumericToRawBytes (biguint64 , newByteLength, isLittleEndian), [[Block]] is buffer.[[ArrayBufferByteLengthData]], [[ByteIndex]] is 0, and [[ElementSize]] is 8 is added to thesurrounding agent 'scandidate execution such that racing calls toSharedArrayBuffer.prototype.groware not "lost", i.e. silently do nothing.
The second requirement above is intentionally vague about how or when the current byte length of buffer is read. Because the byte length must be updated via an atomic read-modify-write operation on the underlying hardware, architectures that use load-link/store-conditional or load-exclusive/store-exclusive instruction pairs may wish to keep the paired instructions close in the instruction stream. As such, SharedArrayBuffer.prototype.grow itself does not perform bounds checking on newByteLength before calling HostGrowSharedArrayBuffer, nor is there a requirement on when the current byte length is read.
This is in contrast with
The default implementation of HostGrowSharedArrayBuffer is to return
25.2.3 The SharedArrayBuffer Constructor
The SharedArrayBuffer
- is %SharedArrayBuffer%.
- is the initial value of the
"SharedArrayBuffer" property of theglobal object , if that property is present (see below). - creates and initializes a new SharedArrayBuffer when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified SharedArrayBuffer behaviour must include asupercall to the SharedArrayBufferconstructor to create and initialize subclass instances with the internal state necessary to support theSharedArrayBuffer.prototypebuilt-in methods.
Whenever a
Unlike an ArrayBuffer, a SharedArrayBuffer cannot become detached, and
its
internal [[ArrayBufferData]] slot is never
25.2.3.1 SharedArrayBuffer ( length [ , options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Let byteLength be ?
ToIndex (length). - Let requestedMaxByteLength be ?
GetArrayBufferMaxByteLengthOption (options). - Return ?
AllocateSharedArrayBuffer (NewTarget, byteLength, requestedMaxByteLength).
25.2.4 Properties of the SharedArrayBuffer Constructor
The SharedArrayBuffer
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
25.2.4.1 SharedArrayBuffer.prototype
The initial value of SharedArrayBuffer.prototype is the
This property has the attributes { [[Writable]]:
25.2.4.2 get SharedArrayBuffer [ @@species ]
SharedArrayBuffer[@@species] is an
- Return the
this value.
The value of the
25.2.5 Properties of the SharedArrayBuffer Prototype Object
The SharedArrayBuffer prototype object:
- is %SharedArrayBuffer.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have an [[ArrayBufferData]] or [[ArrayBufferByteLength]] internal slot.
25.2.5.1 get SharedArrayBuffer.prototype.byteLength
SharedArrayBuffer.prototype.byteLength is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - Let length be
ArrayBufferByteLength (O,seq-cst ). - Return
𝔽 (length).
25.2.5.2 SharedArrayBuffer.prototype.constructor
The initial value of SharedArrayBuffer.prototype.constructor is
25.2.5.3 SharedArrayBuffer.prototype.grow ( newLength )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferMaxByteLength]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - Let newByteLength be ?
ToIndex (newLength). - Let hostHandled be ?
HostGrowSharedArrayBuffer (O, newByteLength). - If hostHandled is
handled , returnundefined . - Let isLittleEndian be the value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Let byteLengthBlock be O.[[ArrayBufferByteLengthData]].
- Let currentByteLengthRawBytes be
GetRawBytesFromSharedBlock (byteLengthBlock, 0,biguint64 ,true ,seq-cst ). - Let newByteLengthRawBytes be
NumericToRawBytes (biguint64 ,ℤ (newByteLength), isLittleEndian). - Repeat,
- NOTE: This is a compare-and-exchange loop to ensure that parallel, racing grows of the same buffer are totally ordered, are not lost, and do not silently do nothing. The loop exits if it was able to attempt to grow uncontended.
- Let currentByteLength be
ℝ (RawBytesToNumeric (biguint64 , currentByteLengthRawBytes, isLittleEndian)). - If newByteLength =
currentByteLength,
return
undefined . - If newByteLength <
currentByteLength
or newByteLength > O.[[ArrayBufferMaxByteLength]], throw a
RangeError exception. - Let byteLengthDelta be newByteLength - currentByteLength.
- If it is impossible to create a new
Shared Data Block value consisting of byteLengthDelta bytes, throw aRangeError exception. - NOTE: No new
Shared Data Block is constructed and used here. The observable behaviour of growable SharedArrayBuffers is specified by allocating amax -sizedShared Data Block at construction time, and this step captures the requirement that implementations that run out of memory must throw aRangeError . - Let readByteLengthRawBytes be
AtomicCompareExchangeInSharedBlock (byteLengthBlock, 0, 8, currentByteLengthRawBytes, newByteLengthRawBytes). - If
ByteListEqual (readByteLengthRawBytes, currentByteLengthRawBytes) istrue , returnundefined . - Set currentByteLengthRawBytes to readByteLengthRawBytes.
Spurious failures of the compare-exchange to update the length are prohibited. If the bounds
checking
for the new length passes and the implementation is not out of memory, a
Parallel calls to SharedArrayBuffer.prototype.grow are totally ordered. For example, consider two
racing calls: sab.grow(10) and sab.grow(20). One of the two calls is
guaranteed to win the race. The call to sab.grow(10) will never shrink
sab
even if sab.grow(20) happened first; in that case it will instead throw a RangeError.
25.2.5.4 get SharedArrayBuffer.prototype.growable
SharedArrayBuffer.prototype.growable is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - If
IsFixedLengthArrayBuffer (O) isfalse , returntrue ; otherwise returnfalse .
25.2.5.5 get SharedArrayBuffer.prototype.maxByteLength
SharedArrayBuffer.prototype.maxByteLength is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - If
IsFixedLengthArrayBuffer (O) istrue , then- Let length be O.[[ArrayBufferByteLength]].
- Else,
- Let length be O.[[ArrayBufferMaxByteLength]].
- Return
𝔽 (length).
25.2.5.6 SharedArrayBuffer.prototype.slice ( start, end )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - Let len be
ArrayBufferByteLength (O,seq-cst ). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let first be 0.
- Else if relativeStart < 0, let first
be
max (len + relativeStart, 0). - Else, let first be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let final be 0.
- Else if relativeEnd < 0, let final
be
max (len + relativeEnd, 0). - Else, let final be
min (relativeEnd, len). - Let newLen be
max (final - first, 0). - Let ctor be ?
SpeciesConstructor (O,%SharedArrayBuffer% ). - Let new be ?
Construct (ctor, «𝔽 (newLen) »). - Perform ?
RequireInternalSlot (new, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (new) isfalse , throw aTypeError exception. - If new.[[ArrayBufferData]]
is O.[[ArrayBufferData]], throw a
TypeError exception. - If
ArrayBufferByteLength (new,seq-cst ) < newLen, throw aTypeError exception. - Let fromBuf be O.[[ArrayBufferData]].
- Let toBuf be new.[[ArrayBufferData]].
- Perform
CopyDataBlockBytes (toBuf, 0, fromBuf, first, newLen). - Return new.
25.2.5.7 SharedArrayBuffer.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
25.2.6 Properties of SharedArrayBuffer Instances
SharedArrayBuffer instances inherit properties from the
SharedArrayBuffer instances, unlike ArrayBuffer instances, are never detached.
25.2.7 Growable SharedArrayBuffer Guidelines
The following are guidelines for ECMAScript programmers working with
We recommend that programs be tested in their deployment environments where possible. The amount of available physical memory differ greatly between hardware devices. Similarly, virtual memory subsystems also differ greatly between hardware devices as well as operating systems. An application that runs without out-of-memory errors on a 64-bit desktop web browser could run out of memory on a 32-bit mobile web browser.
When choosing a value for the
Please note that successfully constructing a
Not all loads of a u8[idx], are not synchronizing. In general, in the absence of
explicit synchronization, one property access being in-bound does not imply a subsequent property
access
in the same length and byteLength getters on
SharedArrayBuffer,
The following are guidelines for ECMAScript implementers implementing
We recommend
Because grow operations can happen in parallel with memory accesses on a
Grown memory must appear zeroed from the moment of its creation, including to any racy accesses in parallel. This can be accomplished via zero-filled-on-demand virtual memory pages, or careful synchronization if manually zeroing memory.
In practice it is difficult to implement
25.3 DataView Objects
25.3.1 Abstract Operations For DataView Objects
25.3.1.1 DataView With Buffer Witness Records
A DataView With Buffer Witness
Record is a
DataView With Buffer Witness Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Object]] | a DataView | The DataView object whose buffer's byte length is loaded. |
| [[CachedBufferByteLength]] |
a non-negative |
The byte length of the object's [[ViewedArrayBuffer]] when the
|
25.3.1.2 MakeDataViewWithBufferWitnessRecord ( obj, order )
The abstract operation MakeDataViewWithBufferWitnessRecord takes arguments obj (a
DataView)
and order (
- Let buffer be obj.[[ViewedArrayBuffer]].
- If
IsDetachedBuffer (buffer) istrue , then- Let byteLength be
detached .
- Let byteLength be
- Else,
- Let byteLength be
ArrayBufferByteLength (buffer, order).
- Let byteLength be
- Return the
DataView With Buffer Witness Record { [[Object]]: obj, [[CachedBufferByteLength]]: byteLength }.
25.3.1.3 GetViewByteLength ( viewRecord )
The abstract operation GetViewByteLength takes argument viewRecord (a
Assert :IsViewOutOfBounds (viewRecord) isfalse .- Let view be viewRecord.[[Object]].
- If view.[[ByteLength]] is
not
auto , return view.[[ByteLength]]. Assert :IsFixedLengthArrayBuffer (view.[[ViewedArrayBuffer]]) isfalse .- Let byteOffset be view.[[ByteOffset]].
- Let byteLength be viewRecord.[[CachedBufferByteLength]].
Assert : byteLength is notdetached .- Return byteLength - byteOffset.
25.3.1.4 IsViewOutOfBounds ( viewRecord )
The abstract operation IsViewOutOfBounds takes argument viewRecord (a
- Let view be viewRecord.[[Object]].
- Let bufferByteLength be viewRecord.[[CachedBufferByteLength]].
Assert :IsDetachedBuffer (view.[[ViewedArrayBuffer]]) istrue if and only if bufferByteLength isdetached .- If bufferByteLength is
detached , returntrue . - Let byteOffsetStart be view.[[ByteOffset]].
- If view.[[ByteLength]] is
auto , then- Let byteOffsetEnd be bufferByteLength.
- Else,
- Let byteOffsetEnd be byteOffsetStart + view.[[ByteLength]].
- If byteOffsetStart >
bufferByteLength
or
byteOffsetEnd > bufferByteLength, return
true . - NOTE: 0-length DataViews are not considered out-of-bounds.
- Return
false .
25.3.1.5 GetViewValue ( view, requestIndex, isLittleEndian, type )
The abstract operation GetViewValue takes arguments view (an
- Perform ?
RequireInternalSlot (view, [[DataView]]). Assert : view has a [[ViewedArrayBuffer]] internal slot.- Let getIndex be ?
ToIndex (requestIndex). - Set isLittleEndian to
ToBoolean (isLittleEndian). - Let viewOffset be view.[[ByteOffset]].
- Let viewRecord be
MakeDataViewWithBufferWitnessRecord (view,unordered ). - NOTE: Bounds checking is not a synchronizing operation when
view's backing buffer is a
growable SharedArrayBuffer . - If
IsViewOutOfBounds (viewRecord) istrue , throw aTypeError exception. - Let viewSize be
GetViewByteLength (viewRecord). - Let elementSize be the Element Size value
specified
in
Table 71 for Element Type type. - If getIndex + elementSize >
viewSize, throw a
RangeError exception. - Let bufferIndex be getIndex + viewOffset.
- Return
GetValueFromBuffer (view.[[ViewedArrayBuffer]], bufferIndex, type,false ,unordered , isLittleEndian).
25.3.1.6 SetViewValue ( view, requestIndex, isLittleEndian, type, value )
The abstract operation SetViewValue takes arguments view (an
- Perform ?
RequireInternalSlot (view, [[DataView]]). Assert : view has a [[ViewedArrayBuffer]] internal slot.- Let getIndex be ?
ToIndex (requestIndex). - If
IsBigIntElementType (type) istrue , let numberValue be ?ToBigInt (value). - Otherwise, let numberValue be ?
ToNumber (value). - Set isLittleEndian to
ToBoolean (isLittleEndian). - Let viewOffset be view.[[ByteOffset]].
- Let viewRecord be
MakeDataViewWithBufferWitnessRecord (view,unordered ). - NOTE: Bounds checking is not a synchronizing operation when
view's backing buffer is a
growable SharedArrayBuffer . - If
IsViewOutOfBounds (viewRecord) istrue , throw aTypeError exception. - Let viewSize be
GetViewByteLength (viewRecord). - Let elementSize be the Element Size value
specified
in
Table 71 for Element Type type. - If getIndex + elementSize >
viewSize, throw a
RangeError exception. - Let bufferIndex be getIndex + viewOffset.
- Perform
SetValueInBuffer (view.[[ViewedArrayBuffer]], bufferIndex, type, numberValue,false ,unordered , isLittleEndian). - Return
undefined .
25.3.2 The DataView Constructor
The DataView
- is %DataView%.
- is the initial value of the
"DataView" property of theglobal object . - creates and initializes a new DataView when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified DataView behaviour must include asupercall to the DataViewconstructor to create and initialize subclass instances with the internal state necessary to support theDataView.prototypebuilt-in methods.
25.3.2.1 DataView ( buffer [ , byteOffset [ , byteLength ] ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Perform ?
RequireInternalSlot (buffer, [[ArrayBufferData]]). - Let offset be ?
ToIndex (byteOffset). - If
IsDetachedBuffer (buffer) istrue , throw aTypeError exception. - Let bufferByteLength be
ArrayBufferByteLength (buffer,seq-cst ). - If offset > bufferByteLength, throw
a
RangeError exception. - Let bufferIsFixedLength be
IsFixedLengthArrayBuffer (buffer). - If byteLength is
undefined , then- If bufferIsFixedLength is
true , then- Let viewByteLength be bufferByteLength - offset.
- Else,
- Let viewByteLength be
auto .
- Let viewByteLength be
- If bufferIsFixedLength is
- Else,
- Let viewByteLength be ?
ToIndex (byteLength). - If offset + viewByteLength >
bufferByteLength, throw a
RangeError exception.
- Let viewByteLength be ?
- Let O be ?
OrdinaryCreateFromConstructor (NewTarget,"%DataView.prototype%" , « [[DataView]], [[ViewedArrayBuffer]], [[ByteLength]], [[ByteOffset]] »). - If
IsDetachedBuffer (buffer) istrue , throw aTypeError exception. - Set bufferByteLength to
ArrayBufferByteLength (buffer,seq-cst ). - If offset > bufferByteLength, throw
a
RangeError exception. - If byteLength is not
undefined , then- If offset + viewByteLength >
bufferByteLength, throw a
RangeError exception.
- If offset + viewByteLength >
bufferByteLength, throw a
- Set O.[[ViewedArrayBuffer]] to buffer.
- Set O.[[ByteLength]] to viewByteLength.
- Set O.[[ByteOffset]] to offset.
- Return O.
25.3.3 Properties of the DataView Constructor
The DataView
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
25.3.3.1 DataView.prototype
The initial value of DataView.prototype is the
This property has the attributes { [[Writable]]:
25.3.4 Properties of the DataView Prototype Object
The DataView prototype object:
- is %DataView.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[DataView]], [[ViewedArrayBuffer]], [[ByteLength]], or [[ByteOffset]] internal slot.
25.3.4.1 get DataView.prototype.buffer
DataView.prototype.buffer is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[DataView]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let buffer be O.[[ViewedArrayBuffer]].
- Return buffer.
25.3.4.2 get DataView.prototype.byteLength
DataView.prototype.byteLength is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[DataView]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let viewRecord be
MakeDataViewWithBufferWitnessRecord (O,seq-cst ). - If
IsViewOutOfBounds (viewRecord) istrue , throw aTypeError exception. - Let size be
GetViewByteLength (viewRecord). - Return
𝔽 (size).
25.3.4.3 get DataView.prototype.byteOffset
DataView.prototype.byteOffset is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[DataView]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let viewRecord be
MakeDataViewWithBufferWitnessRecord (O,seq-cst ). - If
IsViewOutOfBounds (viewRecord) istrue , throw aTypeError exception. - Let offset be O.[[ByteOffset]].
- Return
𝔽 (offset).
25.3.4.4 DataView.prototype.constructor
The initial value of DataView.prototype.constructor is
25.3.4.5 DataView.prototype.getBigInt64 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - Return ?
GetViewValue (v, byteOffset, littleEndian,bigint64 ).
25.3.4.6 DataView.prototype.getBigUint64 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - Return ?
GetViewValue (v, byteOffset, littleEndian,biguint64 ).
25.3.4.7 DataView.prototype.getFloat32 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - If littleEndian is not present, set
littleEndian to
false . - Return ?
GetViewValue (v, byteOffset, littleEndian,float32 ).
25.3.4.8 DataView.prototype.getFloat64 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - If littleEndian is not present, set
littleEndian to
false . - Return ?
GetViewValue (v, byteOffset, littleEndian,float64 ).
25.3.4.9 DataView.prototype.getInt8 ( byteOffset )
This method performs the following steps when called:
- Let v be the
this value. - Return ?
GetViewValue (v, byteOffset,true ,int8 ).
25.3.4.10 DataView.prototype.getInt16 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - If littleEndian is not present, set
littleEndian to
false . - Return ?
GetViewValue (v, byteOffset, littleEndian,int16 ).
25.3.4.11 DataView.prototype.getInt32 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - If littleEndian is not present, set
littleEndian to
false . - Return ?
GetViewValue (v, byteOffset, littleEndian,int32 ).
25.3.4.12 DataView.prototype.getUint8 ( byteOffset )
This method performs the following steps when called:
- Let v be the
this value. - Return ?
GetViewValue (v, byteOffset,true ,uint8 ).
25.3.4.13 DataView.prototype.getUint16 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - If littleEndian is not present, set
littleEndian to
false . - Return ?
GetViewValue (v, byteOffset, littleEndian,uint16 ).
25.3.4.14 DataView.prototype.getUint32 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - If littleEndian is not present, set
littleEndian to
false . - Return ?
GetViewValue (v, byteOffset, littleEndian,uint32 ).
25.3.4.15 DataView.prototype.setBigInt64 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - Return ?
SetViewValue (v, byteOffset, littleEndian,bigint64 , value).
25.3.4.16 DataView.prototype.setBigUint64 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - Return ?
SetViewValue (v, byteOffset, littleEndian,biguint64 , value).
25.3.4.17 DataView.prototype.setFloat32 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - If littleEndian is not present, set
littleEndian to
false . - Return ?
SetViewValue (v, byteOffset, littleEndian,float32 , value).
25.3.4.18 DataView.prototype.setFloat64 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - If littleEndian is not present, set
littleEndian to
false . - Return ?
SetViewValue (v, byteOffset, littleEndian,float64 , value).
25.3.4.19 DataView.prototype.setInt8 ( byteOffset, value )
This method performs the following steps when called:
- Let v be the
this value. - Return ?
SetViewValue (v, byteOffset,true ,int8 , value).
25.3.4.20 DataView.prototype.setInt16 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - If littleEndian is not present, set
littleEndian to
false . - Return ?
SetViewValue (v, byteOffset, littleEndian,int16 , value).
25.3.4.21 DataView.prototype.setInt32 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - If littleEndian is not present, set
littleEndian to
false . - Return ?
SetViewValue (v, byteOffset, littleEndian,int32 , value).
25.3.4.22 DataView.prototype.setUint8 ( byteOffset, value )
This method performs the following steps when called:
- Let v be the
this value. - Return ?
SetViewValue (v, byteOffset,true ,uint8 , value).
25.3.4.23 DataView.prototype.setUint16 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - If littleEndian is not present, set
littleEndian to
false . - Return ?
SetViewValue (v, byteOffset, littleEndian,uint16 , value).
25.3.4.24 DataView.prototype.setUint32 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let v be the
this value. - If littleEndian is not present, set
littleEndian to
false . - Return ?
SetViewValue (v, byteOffset, littleEndian,uint32 , value).
25.3.4.25 DataView.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
25.3.5 Properties of DataView Instances
DataView instances are
The value of the [[DataView]] internal slot is not used within this
specification. The simple presence of that internal slot is used within the specification to
identify
objects created using the DataView
25.4 The Atomics Object
The Atomics object:
- is %Atomics%.
- is the initial value of the
"Atomics" property of theglobal object . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Object.prototype% . - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a [[Call]] internal method; it cannot be invoked as a function.
The Atomics object provides functions that operate indivisibly (atomically) on shared memory array cells
as
well as functions that let
For informative guidelines for programming and implementing shared memory in ECMAScript, please see
the
notes at the end of the
25.4.1 Waiter Record
A Waiter Record is a Atomics.wait or Atomics.waitAsync.
A Waiter Record has fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[AgentSignifier]] |
an |
The Atomics.wait or Atomics.waitAsync.
|
| [[PromiseCapability]] |
a |
If denoting a call to Atomics.waitAsync, the resulting promise, otherwise
|
| [[TimeoutTime]] |
a non-negative |
The earliest time by which timeout may be triggered; computed using |
| [[Result]] |
|
The return value of the call. |
25.4.2 WaiterList Records
A WaiterList Record is used to explain waiting
and
notification of Atomics.wait,
Atomics.waitAsync, and Atomics.notify.
A WaiterList Record has fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Waiters]] |
a |
The calls to Atomics.wait or Atomics.waitAsync that are waiting on
the
location with which this WaiterList is associated.
|
| [[MostRecentLeaveEvent]] |
a |
The event of the most recent leaving of its |
There can be multiple
The
Each WaiterList Record has a critical section
that
controls exclusive access to that WaiterList Record during evaluation. Only a single
25.4.3 Abstract Operations for Atomics
25.4.3.1 ValidateIntegerTypedArray ( typedArray, waitable )
The abstract operation ValidateIntegerTypedArray takes arguments typedArray (an
- Let taRecord be ?
ValidateTypedArray (typedArray,unordered ). - NOTE: Bounds checking is not a synchronizing operation when
typedArray's backing buffer is a
growable SharedArrayBuffer . - If waitable is
true , then- If typedArray.[[TypedArrayName]] is neither
"Int32Array" nor"BigInt64Array" , throw aTypeError exception.
- If typedArray.[[TypedArrayName]] is neither
- Else,
- Let type be
TypedArrayElementType (typedArray). - If
IsUnclampedIntegerElementType (type) isfalse andIsBigIntElementType (type) isfalse , throw aTypeError exception.
- Let type be
- Return taRecord.
25.4.3.2 ValidateAtomicAccess ( taRecord, requestIndex )
The abstract operation ValidateAtomicAccess takes arguments taRecord (a
- Let length be
TypedArrayLength (taRecord). - Let accessIndex be ?
ToIndex (requestIndex). Assert : accessIndex ≥ 0.- If accessIndex ≥ length, throw a
RangeError exception. - Let typedArray be taRecord.[[Object]].
- Let elementSize be
TypedArrayElementSize (typedArray). - Let offset be typedArray.[[ByteOffset]].
- Return (accessIndex × elementSize) + offset.
25.4.3.3 ValidateAtomicAccessOnIntegerTypedArray ( typedArray, requestIndex [ , waitable ] )
The abstract operation ValidateAtomicAccessOnIntegerTypedArray takes arguments typedArray
(an
- If waitable is not present, set
waitable
to
false . - Let taRecord be ?
ValidateIntegerTypedArray (typedArray, waitable). - Return ?
ValidateAtomicAccess (taRecord, requestIndex).
25.4.3.4 RevalidateAtomicAccess ( typedArray, byteIndexInBuffer )
The abstract operation RevalidateAtomicAccess takes arguments typedArray (a
- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (typedArray,unordered ). - NOTE: Bounds checking is not a synchronizing operation when
typedArray's backing buffer is a
growable SharedArrayBuffer . - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. Assert : byteIndexInBuffer ≥ typedArray.[[ByteOffset]].- If byteIndexInBuffer ≥ taRecord.[[CachedBufferByteLength]], throw a
RangeError exception. - Return
unused .
25.4.3.5 GetWaiterList ( block, i )
The abstract operation GetWaiterList takes arguments block (a
Assert : i and i + 3 are valid byte offsets within the memory of block.- Return the
WaiterList Record that is referenced by the pair (block, i).
25.4.3.6 EnterCriticalSection ( WL )
The abstract operation EnterCriticalSection takes argument WL (a
Assert : Thesurrounding agent is not in thecritical section for anyWaiterList Record .- Wait until no
agent is in thecritical section for WL, then enter thecritical section for WL (without allowing any otheragent to enter). - If WL.[[MostRecentLeaveEvent]] is not
empty , then- NOTE: A WL whose
critical section has been entered at least once has aSynchronize event set byLeaveCriticalSection . - Let execution be the [[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - Let enterEvent be a new
Synchronize event . - Append enterEvent to eventsRecord.[[EventList]].
- Append (WL.[[MostRecentLeaveEvent]], enterEvent) to eventsRecord.[[AgentSynchronizesWith]].
- NOTE: A WL whose
- Return
unused .
EnterCriticalSection has contention when an
25.4.3.7 LeaveCriticalSection ( WL )
The abstract operation LeaveCriticalSection takes argument WL (a
Assert : Thesurrounding agent is in thecritical section for WL.- Let execution be the [[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - Let leaveEvent be a new
Synchronize event . - Append leaveEvent to eventsRecord.[[EventList]].
- Set WL.[[MostRecentLeaveEvent]] to leaveEvent.
- Leave the
critical section for WL. - Return
unused .
25.4.3.8 AddWaiter ( WL, waiterRecord )
The abstract operation AddWaiter takes arguments WL (a
Assert : Thesurrounding agent is in thecritical section for WL.Assert : There is noWaiter Record in WL.[[Waiters]] whose [[PromiseCapability]] field is waiterRecord.[[PromiseCapability]] and whose [[AgentSignifier]] field is waiterRecord.[[AgentSignifier]].- Append waiterRecord to WL.[[Waiters]].
- Return
unused .
25.4.3.9 RemoveWaiter ( WL, waiterRecord )
The abstract operation RemoveWaiter takes arguments WL (a
Assert : Thesurrounding agent is in thecritical section for WL.Assert : WL.[[Waiters]] contains waiterRecord.- Remove waiterRecord from WL.[[Waiters]].
- Return
unused .
25.4.3.10 RemoveWaiters ( WL, c )
The abstract operation RemoveWaiters takes arguments WL (a
Assert : Thesurrounding agent is in thecritical section for WL.- Let len be the number of elements in WL.[[Waiters]].
- Let n be
min (c, len). - Let L be a
List whose elements are the first n elements of WL.[[Waiters]]. - Remove the first n elements of WL.[[Waiters]].
- Return L.
25.4.3.11 SuspendThisAgent ( WL, waiterRecord )
The abstract operation SuspendThisAgent takes arguments WL (a
Assert : Thesurrounding agent is in thecritical section for WL.Assert : WL.[[Waiters]] contains waiterRecord.- Let thisAgent be
AgentSignifier (). Assert : waiterRecord.[[AgentSignifier]] is thisAgent.Assert : waiterRecord.[[PromiseCapability]] isblocking .Assert :AgentCanSuspend () istrue .- Perform
LeaveCriticalSection (WL) and suspend thesurrounding agent until the time is waiterRecord.[[TimeoutTime]], performing the combined operation in such a way that a notification that arrives after thecritical section is exited but before the suspension takes effect is not lost. Thesurrounding agent can only wake from suspension due to a timeout or due to anotheragent callingNotifyWaiter with arguments WL and thisAgent (i.e. via a call toAtomics.notify). - Perform
EnterCriticalSection (WL). - Return
unused .
25.4.3.12 NotifyWaiter ( WL, waiterRecord )
The abstract operation NotifyWaiter takes arguments WL (a
Assert : Thesurrounding agent is in thecritical section for WL.- If waiterRecord.[[PromiseCapability]] is
blocking , then- Wake the
agent whose signifier is waiterRecord.[[AgentSignifier]] from suspension. - NOTE: This causes the
agent to resume execution inSuspendThisAgent .
- Wake the
- Else if
AgentSignifier () is waiterRecord.[[AgentSignifier]], then- Let promiseCapability be waiterRecord.[[PromiseCapability]].
- Perform !
Call (promiseCapability.[[Resolve]],undefined , « waiterRecord.[[Result]] »).
- Else,
- Perform
EnqueueResolveInAgentJob (waiterRecord.[[AgentSignifier]], waiterRecord.[[PromiseCapability]], waiterRecord.[[Result]]).
- Perform
- Return
unused .
25.4.3.13 EnqueueResolveInAgentJob ( agentSignifier, promiseCapability, resolution )
The abstract operation EnqueueResolveInAgentJob takes arguments agentSignifier (an
- Let resolveJob be a new
Job Abstract Closure with no parameters that captures agentSignifier, promiseCapability, and resolution and performs the following steps when called:Assert :AgentSignifier () is agentSignifier.- Perform !
Call (promiseCapability.[[Resolve]],undefined , « resolution »). - Return
unused .
- Let realmInTargetAgent be !
GetFunctionRealm (promiseCapability.[[Resolve]]). Assert : agentSignifier is realmInTargetAgent.[[AgentSignifier]].- Perform
HostEnqueueGenericJob (resolveJob, realmInTargetAgent). - Return
unused .
25.4.3.14 DoWait ( mode, typedArray, index, value, timeout )
The abstract operation DoWait takes arguments mode (
- Let taRecord be ?
ValidateIntegerTypedArray (typedArray,true ). - Let buffer be taRecord.[[Object]].[[ViewedArrayBuffer]].
- If
IsSharedArrayBuffer (buffer) isfalse , throw aTypeError exception. - Let i be ?
ValidateAtomicAccess (taRecord, index). - Let arrayTypeName be typedArray.[[TypedArrayName]].
- If arrayTypeName is
"BigInt64Array" , let v be ?ToBigInt64 (value). - Else, let v be ?
ToInt32 (value). - Let q be ?
ToNumber (timeout). - If q is either
NaN or+∞ 𝔽, let t be +∞; else if q is-∞ 𝔽, let t be 0; else let t bemax (ℝ (q), 0). - If mode is
sync andAgentCanSuspend () isfalse , throw aTypeError exception. - Let block be buffer.[[ArrayBufferData]].
- Let offset be typedArray.[[ByteOffset]].
- Let byteIndexInBuffer be (i × 4) + offset.
- Let WL be
GetWaiterList (block, byteIndexInBuffer). - If mode is
sync , then- Let promiseCapability be
blocking . - Let resultObject be
undefined .
- Let promiseCapability be
- Else,
- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let resultObject be
OrdinaryObjectCreate (%Object.prototype% ).
- Let promiseCapability be !
- Perform
EnterCriticalSection (WL). - Let elementType be
TypedArrayElementType (typedArray). - Let w be
GetValueFromBuffer (buffer, byteIndexInBuffer, elementType,true ,seq-cst ). - If v ≠ w, then
- Perform
LeaveCriticalSection (WL). - If mode is
sync , return"not-equal" . - Perform !
CreateDataPropertyOrThrow (resultObject,"async" ,false ). - Perform !
CreateDataPropertyOrThrow (resultObject,"value" ,"not-equal" ). - Return resultObject.
- Perform
- If t is 0 and mode is
async , then- NOTE: There is no special handling of synchronous immediate timeouts. Asynchronous immediate timeouts have special handling in order to fail fast and avoid unnecessary Promise jobs.
- Perform
LeaveCriticalSection (WL). - Perform !
CreateDataPropertyOrThrow (resultObject,"async" ,false ). - Perform !
CreateDataPropertyOrThrow (resultObject,"value" ,"timed-out" ). - Return resultObject.
- Let thisAgent be
AgentSignifier (). - Let now be the
time value (UTC) identifying the current time. - Let additionalTimeout be an
implementation-defined non-negativemathematical value . - Let timeoutTime be
ℝ (now) + t + additionalTimeout. - NOTE: When t is +∞, timeoutTime is also +∞.
- Let waiterRecord be a new
Waiter Record { [[AgentSignifier]]: thisAgent, [[PromiseCapability]]: promiseCapability, [[TimeoutTime]]: timeoutTime, [[Result]]:"ok" }. - Perform
AddWaiter (WL, waiterRecord). - If mode is
sync , then- Perform
SuspendThisAgent (WL, waiterRecord).
- Perform
- Else if timeoutTime is
finite , then- Perform
EnqueueAtomicsWaitAsyncTimeoutJob (WL, waiterRecord).
- Perform
- Perform
LeaveCriticalSection (WL). - If mode is
sync , return waiterRecord.[[Result]]. - Perform !
CreateDataPropertyOrThrow (resultObject,"async" ,true ). - Perform !
CreateDataPropertyOrThrow (resultObject,"value" , promiseCapability.[[Promise]]). - Return resultObject.
additionalTimeout allows implementations to pad timeouts as necessary, such as for reducing power consumption or coarsening timer resolution to mitigate timing attacks. This value may differ from call to call of DoWait.
25.4.3.15 EnqueueAtomicsWaitAsyncTimeoutJob ( WL, waiterRecord )
The abstract operation EnqueueAtomicsWaitAsyncTimeoutJob takes arguments WL (a
- Let timeoutJob be a new
Job Abstract Closure with no parameters that captures WL and waiterRecord and performs the following steps when called:- Perform
EnterCriticalSection (WL). - If WL.[[Waiters]]
contains waiterRecord, then
- Let timeOfJobExecution be the
time value (UTC) identifying the current time. Assert :ℝ (timeOfJobExecution) ≥ waiterRecord.[[TimeoutTime]] (ignoring potential non-monotonicity oftime values ).- Set waiterRecord.[[Result]] to
"timed-out" . - Perform
RemoveWaiter (WL, waiterRecord). - Perform
NotifyWaiter (WL, waiterRecord).
- Let timeOfJobExecution be the
- Perform
LeaveCriticalSection (WL). - Return
unused .
- Perform
- Let now be the
time value (UTC) identifying the current time. - Let currentRealm be
the current Realm Record . - Perform
HostEnqueueTimeoutJob (timeoutJob, currentRealm,𝔽 (waiterRecord.[[TimeoutTime]]) - now). - Return
unused .
25.4.3.16 AtomicCompareExchangeInSharedBlock ( block, byteIndexInBuffer, elementSize, expectedBytes, replacementBytes )
The abstract operation AtomicCompareExchangeInSharedBlock takes arguments block (a
- Let execution be the [[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - Let rawBytesRead be a
List of length elementSize whose elements are nondeterministically chosenbyte values . - NOTE: In implementations, rawBytesRead is the
result
of a load-link, of a load-exclusive, or of an operand of a read-modify-write instruction on the
underlying hardware. The nondeterminism is a semantic prescription of the
memory model to describe observable behaviour of hardware with weak consistency. - NOTE: The comparison of the expected value and the read value
is
performed outside of the
read-modify-write modification function to avoid needlessly strong synchronization when the expected value is not equal to the read value. - If
ByteListEqual (rawBytesRead, expectedBytes) istrue , then- Let second be a new
read-modify-write modification function with parameters (oldBytes, newBytes) that captures nothing and performs the following steps atomically when called:- Return newBytes.
- Let event be
ReadModifyWriteSharedMemory { [[Order]]:seq-cst , [[NoTear]]:true , [[Block]]: block, [[ByteIndex]]: byteIndexInBuffer, [[ElementSize]]: elementSize, [[Payload]]: replacementBytes, [[ModifyOp]]: second }.
- Let second be a new
- Else,
- Let event be
ReadSharedMemory { [[Order]]:seq-cst , [[NoTear]]:true , [[Block]]: block, [[ByteIndex]]: byteIndexInBuffer, [[ElementSize]]: elementSize }.
- Let event be
- Append event to eventsRecord.[[EventList]].
- Append
Chosen Value Record { [[Event]]: event, [[ChosenValue]]: rawBytesRead } to execution.[[ChosenValues]]. - Return rawBytesRead.
25.4.3.17 AtomicReadModifyWrite ( typedArray, index, value, op )
The abstract operation AtomicReadModifyWrite takes arguments typedArray (an
- Let byteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray, index). - If typedArray.[[ContentType]]
is
bigint , let v be ?ToBigInt (value). - Otherwise, let v be
𝔽 (?ToIntegerOrInfinity (value)). - Perform ?
RevalidateAtomicAccess (typedArray, byteIndexInBuffer). - Let buffer be typedArray.[[ViewedArrayBuffer]].
- Let elementType be
TypedArrayElementType (typedArray). - Return
GetModifySetValueInBuffer (buffer, byteIndexInBuffer, elementType, v, op).
25.4.3.18 ByteListBitwiseOp ( op, xBytes, yBytes )
The abstract operation ByteListBitwiseOp takes arguments op (&,
^, or |), xBytes (a
Assert : xBytes and yBytes have the same number of elements.- Let result be a new empty
List . - Let i be 0.
- For each element xByte of xBytes, do
- Let yByte be yBytes[i].
- If op is
&, then- Let resultByte be the result of applying the bitwise AND operation to xByte and yByte.
- Else if op is
^, then- Let resultByte be the result of applying the bitwise exclusive OR (XOR) operation to xByte and yByte.
- Else,
Assert : op is|.- Let resultByte be the result of applying the bitwise inclusive OR operation to xByte and yByte.
- Set i to i + 1.
- Append resultByte to result.
- Return result.
25.4.3.19 ByteListEqual ( xBytes, yBytes )
The abstract operation ByteListEqual takes arguments xBytes (a
- If xBytes and yBytes do not have the
same
number of elements, return
false . - Let i be 0.
- For each element xByte of xBytes, do
- Let yByte be yBytes[i].
- If xByte ≠ yByte, return
false . - Set i to i + 1.
- Return
true .
25.4.4 Atomics.add ( typedArray, index, value )
This function performs the following steps when called:
- Let type be
TypedArrayElementType (typedArray). - Let isLittleEndian be the value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Let add be a new
read-modify-write modification function with parameters (xBytes, yBytes) that captures type and isLittleEndian and performs the following steps atomically when called:- Let x be
RawBytesToNumeric (type, xBytes, isLittleEndian). - Let y be
RawBytesToNumeric (type, yBytes, isLittleEndian). - If x
is a Number , then- Let sum be
Number::add (x, y).
- Let sum be
- Else,
Assert : xis a BigInt .- Let sum be
BigInt::add (x, y).
- Let sumBytes be
NumericToRawBytes (type, sum, isLittleEndian). Assert : sumBytes, xBytes, and yBytes have the same number of elements.- Return sumBytes.
- Let x be
- Return ?
AtomicReadModifyWrite (typedArray, index, value, add).
25.4.5 Atomics.and ( typedArray, index, value )
This function performs the following steps when called:
- Let and be a new
read-modify-write modification function with parameters (xBytes, yBytes) that captures nothing and performs the following steps atomically when called:- Return
ByteListBitwiseOp (&, xBytes, yBytes).
- Return
- Return ?
AtomicReadModifyWrite (typedArray, index, value, and).
25.4.6 Atomics.compareExchange ( typedArray, index, expectedValue, replacementValue )
This function performs the following steps when called:
- Let byteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray, index). - Let buffer be typedArray.[[ViewedArrayBuffer]].
- Let block be buffer.[[ArrayBufferData]].
- If typedArray.[[ContentType]]
is
bigint , then - Else,
- Let expected be
𝔽 (?ToIntegerOrInfinity (expectedValue)). - Let replacement be
𝔽 (?ToIntegerOrInfinity (replacementValue)).
- Let expected be
- Perform ?
RevalidateAtomicAccess (typedArray, byteIndexInBuffer). - Let elementType be
TypedArrayElementType (typedArray). - Let elementSize be
TypedArrayElementSize (typedArray). - Let isLittleEndian be the value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Let expectedBytes be
NumericToRawBytes (elementType, expected, isLittleEndian). - Let replacementBytes be
NumericToRawBytes (elementType, replacement, isLittleEndian). - If
IsSharedArrayBuffer (buffer) istrue , then- Let rawBytesRead be
AtomicCompareExchangeInSharedBlock (block, byteIndexInBuffer, elementSize, expectedBytes, replacementBytes).
- Let rawBytesRead be
- Else,
- Let rawBytesRead be a
List of length elementSize whose elements are the sequence of elementSize bytes starting with block[byteIndexInBuffer]. - If
ByteListEqual (rawBytesRead, expectedBytes) istrue , then- Store the individual bytes of replacementBytes into block, starting at block[byteIndexInBuffer].
- Let rawBytesRead be a
- Return
RawBytesToNumeric (elementType, rawBytesRead, isLittleEndian).
25.4.7 Atomics.exchange ( typedArray, index, value )
This function performs the following steps when called:
- Let second be a new
read-modify-write modification function with parameters (oldBytes, newBytes) that captures nothing and performs the following steps atomically when called:- Return newBytes.
- Return ?
AtomicReadModifyWrite (typedArray, index, value, second).
25.4.8 Atomics.isLockFree ( size )
This function performs the following steps when called:
- Let n be ?
ToIntegerOrInfinity (size). - Let AR be the
Agent Record of thesurrounding agent . - If n = 1, return AR.[[IsLockFree1]].
- If n = 2, return AR.[[IsLockFree2]].
- If n = 4, return
true . - If n = 8, return AR.[[IsLockFree8]].
- Return
false .
This function is an optimization primitive. The intuition is that if the atomic step of an atomic
primitive (compareExchange, load, store, add,
sub, and, or, xor, or exchange) on
a
datum of size n bytes will be performed without the Atomics.isLockFree(n) will return
Atomics.isLockFree(4) always returns
Regardless of the value returned by this function, all atomic operations are guaranteed to be atomic. For example, they will never have a visible operation take place in the middle of the operation (e.g., "tearing").
25.4.9 Atomics.load ( typedArray, index )
This function performs the following steps when called:
- Let byteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray, index). - Perform ?
RevalidateAtomicAccess (typedArray, byteIndexInBuffer). - Let buffer be typedArray.[[ViewedArrayBuffer]].
- Let elementType be
TypedArrayElementType (typedArray). - Return
GetValueFromBuffer (buffer, byteIndexInBuffer, elementType,true ,seq-cst ).
25.4.10 Atomics.or ( typedArray, index, value )
This function performs the following steps when called:
- Let or be a new
read-modify-write modification function with parameters (xBytes, yBytes) that captures nothing and performs the following steps atomically when called:- Return
ByteListBitwiseOp (|, xBytes, yBytes).
- Return
- Return ?
AtomicReadModifyWrite (typedArray, index, value, or).
25.4.11 Atomics.store ( typedArray, index, value )
This function performs the following steps when called:
- Let byteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray, index). - If typedArray.[[ContentType]]
is
bigint , let v be ?ToBigInt (value). - Otherwise, let v be
𝔽 (?ToIntegerOrInfinity (value)). - Perform ?
RevalidateAtomicAccess (typedArray, byteIndexInBuffer). - Let buffer be typedArray.[[ViewedArrayBuffer]].
- Let elementType be
TypedArrayElementType (typedArray). - Perform
SetValueInBuffer (buffer, byteIndexInBuffer, elementType, v,true ,seq-cst ). - Return v.
25.4.12 Atomics.sub ( typedArray, index, value )
This function performs the following steps when called:
- Let type be
TypedArrayElementType (typedArray). - Let isLittleEndian be the value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Let subtract be a new
read-modify-write modification function with parameters (xBytes, yBytes) that captures type and isLittleEndian and performs the following steps atomically when called:- Let x be
RawBytesToNumeric (type, xBytes, isLittleEndian). - Let y be
RawBytesToNumeric (type, yBytes, isLittleEndian). - If x
is a Number , then- Let difference be
Number::subtract (x, y).
- Let difference be
- Else,
Assert : xis a BigInt .- Let difference be
BigInt::subtract (x, y).
- Let differenceBytes be
NumericToRawBytes (type, difference, isLittleEndian). Assert : differenceBytes, xBytes, and yBytes have the same number of elements.- Return differenceBytes.
- Let x be
- Return ?
AtomicReadModifyWrite (typedArray, index, value, subtract).
25.4.13 Atomics.wait ( typedArray, index, value, timeout )
This function puts the
It performs the following steps when called:
- Return ?
DoWait (sync , typedArray, index, value, timeout).
25.4.14 Atomics.waitAsync ( typedArray, index, value, timeout )
This function returns a Promise that is resolved when the calling
It performs the following steps when called:
- Return ?
DoWait (async , typedArray, index, value, timeout).
25.4.15 Atomics.notify ( typedArray, index, count )
This function notifies some
It performs the following steps when called:
- Let byteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray, index,true ). - If count is
undefined , then- Let c be +∞.
- Else,
- Let intCount be ?
ToIntegerOrInfinity (count). - Let c be
max (intCount, 0).
- Let intCount be ?
- Let buffer be typedArray.[[ViewedArrayBuffer]].
- Let block be buffer.[[ArrayBufferData]].
- If
IsSharedArrayBuffer (buffer) isfalse , return+0 𝔽. - Let WL be
GetWaiterList (block, byteIndexInBuffer). - Perform
EnterCriticalSection (WL). - Let S be
RemoveWaiters (WL, c). - For each element W of S, do
- Perform
NotifyWaiter (WL, W).
- Perform
- Perform
LeaveCriticalSection (WL). - Let n be the number of elements in S.
- Return
𝔽 (n).
25.4.16 Atomics.xor ( typedArray, index, value )
This function performs the following steps when called:
- Let xor be a new
read-modify-write modification function with parameters (xBytes, yBytes) that captures nothing and performs the following steps atomically when called:- Return
ByteListBitwiseOp (^, xBytes, yBytes).
- Return
- Return ?
AtomicReadModifyWrite (typedArray, index, value, xor).
25.4.17 Atomics [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
25.5 The JSON Object
The JSON object:
- is %JSON%.
- is the initial value of the
"JSON" property of theglobal object . - is an
ordinary object . - contains two functions,
parseandstringify, that are used to parse and construct JSON texts. - has a [[Prototype]] internal slot whose value is
%Object.prototype% . - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a [[Call]] internal method; it cannot be invoked as a function.
The JSON Data Interchange Format is defined in ECMA-404. The JSON interchange format used in this
specification is exactly that described by ECMA-404. Conforming implementations of JSON.parse
and
JSON.stringify must support the exact interchange format described in the ECMA-404
specification
without any deletions or extensions to the format.
25.5.1 JSON.parse ( text [ , reviver ] )
This function parses a JSON text (a JSON-formatted String) and produces an
The optional reviver parameter is a function that takes two parameters, key and
value. It can filter and transform the results. It is called with each of the
key/value pairs produced by the parse, and its return value is used instead of the
original value. If it returns what it received, the structure is not modified. If it returns
- Let jsonString be ?
ToString (text). - Parse
StringToCodePoints (jsonString) as a JSON text as specified in ECMA-404. Throw aSyntaxError exception if it is not a valid JSON text as defined in that specification. - Let scriptString be the
string-concatenation of"(" , jsonString, and");" . - Let script be
ParseText (StringToCodePoints (scriptString),Script ). - NOTE: The
early error rules defined in13.2.5.1 have special handling for the above invocation ofParseText . Assert : script is aParse Node .- Let completion be
Completion (Evaluation of script). - NOTE: The
PropertyDefinitionEvaluation semantics defined in13.2.5.5 have special handling for the above evaluation. - Let unfiltered be completion.[[Value]].
Assert : unfiltered is either a String, a Number, a Boolean, an Object that is defined by either anArrayLiteral or anObjectLiteral , ornull .- If
IsCallable (reviver) istrue , then- Let root be
OrdinaryObjectCreate (%Object.prototype% ). - Let rootName be the empty String.
- Perform !
CreateDataPropertyOrThrow (root, rootName, unfiltered). - Return ?
InternalizeJSONProperty (root, rootName, reviver).
- Let root be
- Else,
- Return unfiltered.
The
Valid JSON text is a subset of the ECMAScript
However, because JSON.parse, the same source text can produce different
results
when evaluated as a JSON.parse, means that not all
texts
accepted by JSON.parse are valid as a
25.5.1.1 InternalizeJSONProperty ( holder, name, reviver )
The abstract operation InternalizeJSONProperty takes arguments holder (an Object),
name (a String), and reviver (a
This algorithm intentionally does not throw an exception if either [[Delete]] or
It performs the following steps when called:
- Let val be ?
Get (holder, name). - If val
is an Object , then- Let isArray be ?
IsArray (val). - If isArray is
true , then- Let len be ?
LengthOfArrayLike (val). - Let I be 0.
- Repeat, while I < len,
- Let prop be !
ToString (𝔽 (I)). - Let newElement be ?
InternalizeJSONProperty (val, prop, reviver). - If newElement is
undefined , then- Perform ? val.[[Delete]](prop).
- Else,
- Perform ?
CreateDataProperty (val, prop, newElement).
- Perform ?
- Set I to I + 1.
- Let prop be !
- Let len be ?
- Else,
- Let keys be ?
EnumerableOwnProperties (val,key ). - For each String P of keys, do
- Let newElement be ?
InternalizeJSONProperty (val, P, reviver). - If newElement is
undefined , then- Perform ? val.[[Delete]](P).
- Else,
- Perform ?
CreateDataProperty (val, P, newElement).
- Perform ?
- Let newElement be ?
- Let keys be ?
- Let isArray be ?
- Return ?
Call (reviver, holder, « name, val »).
It is not permitted for a conforming implementation of JSON.parse to extend the JSON
grammars. If an implementation wishes to support a modified or extended JSON interchange format it
must
do
so by defining a different parse function.
In the case where there are duplicate name Strings within an object, lexically preceding values for the same key shall be overwritten.
25.5.2 JSON.stringify ( value [ , replacer [ , space ] ] )
This function returns a String in UTF-16 encoded JSON format representing an
It performs the following steps when called:
- Let stack be a new empty
List . - Let indent be the empty String.
- Let PropertyList be
undefined . - Let ReplacerFunction be
undefined . - If replacer
is an Object , then- If
IsCallable (replacer) istrue , then- Set ReplacerFunction to replacer.
- Else,
- Let isArray be ?
IsArray (replacer). - If isArray is
true , then- Set PropertyList to a new empty
List . - Let len be ?
LengthOfArrayLike (replacer). - Let k be 0.
- Repeat, while k < len,
- Let prop be !
ToString (𝔽 (k)). - Let v be ?
Get (replacer, prop). - Let item be
undefined . - If v
is a String , then- Set item to v.
- Else if v
is a Number , then- Set item to !
ToString (v).
- Set item to !
- Else if v
is an Object , then- If v has a [[StringData]] or [[NumberData]]
internal slot, set item to ?
ToString (v).
- If v has a [[StringData]] or [[NumberData]]
internal slot, set item to ?
- If item is not
undefined and PropertyList does not contain item, then- Append item to PropertyList.
- Set k to k + 1.
- Let prop be !
- Set PropertyList to a new empty
- Let isArray be ?
- If
- If space
is an Object , then - If space
is a Number , then- Let spaceMV be !
ToIntegerOrInfinity (space). - Set spaceMV to
min (10, spaceMV). - If spaceMV < 1, let gap be the empty String; otherwise let gap be the String value containing spaceMV occurrences of the code unit 0x0020 (SPACE).
- Let spaceMV be !
- Else if space
is a String , then- If the length of space ≤ 10, let gap
be
space; otherwise let gap be the
substring of space from 0 to 10.
- If the length of space ≤ 10, let gap
be
space; otherwise let gap be the
- Else,
- Let gap be the empty String.
- Let wrapper be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (wrapper, the empty String, value). - Let state be the
JSON Serialization Record { [[ReplacerFunction]]: ReplacerFunction, [[Stack]]: stack, [[Indent]]: indent, [[Gap]]: gap, [[PropertyList]]: PropertyList }. - Return ?
SerializeJSONProperty (state, the empty String, wrapper).
The
JSON structures are allowed to be nested to any depth, but they must be acyclic. If
value
is
or contains a cyclic structure, then this function must throw a
a = [];
a[0] = a;
my_text = JSON.stringify(a); // This must throw a TypeError.Symbolic primitive values are rendered as follows:
-
The
null value is rendered in JSON text as the String value"null" . -
The
undefined value is not rendered. -
The
true value is rendered in JSON text as the String value"true" . -
The
false value is rendered in JSON text as the String value"false" .
String values are wrapped in QUOTATION MARK (") code units. The code units
"
and \ are escaped with \ prefixes. Control characters code units are
replaced
with escape sequences \uHHHH, or with the shorter forms, \b (BACKSPACE),
\f (FORM FEED), \n (LINE FEED), \r (CARRIAGE RETURN),
\t (CHARACTER TABULATION).
Values that do not have a JSON representation (such as
An object is rendered as U+007B (LEFT CURLY BRACKET) followed by zero or more properties, separated
with a U+002C (COMMA), closed with a U+007D (RIGHT CURLY BRACKET). A property is a quoted String
representing the
25.5.2.1 JSON Serialization Record
A JSON Serialization Record is a
JSON Serialization Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[ReplacerFunction]] | a |
A function that can supply replacement values for object properties (from JSON.stringify's replacer parameter). |
| [[PropertyList]] | either a |
The names of properties to include when serializing a non-array object (from JSON.stringify's replacer parameter). |
| [[Gap]] | a String | The unit of indentation (from JSON.stringify's space parameter). |
| [[Stack]] | a |
The set of nested objects that are in the process of being serialized. Used to detect cyclic structures. |
| [[Indent]] | a String | The current indentation. |
25.5.2.2 SerializeJSONProperty ( state, key, holder )
The abstract operation SerializeJSONProperty takes arguments state (a
- Let value be ?
Get (holder, key). - If value
is an Object or valueis a BigInt , then- Let toJSON be ?
GetV (value,"toJSON" ). - If
IsCallable (toJSON) istrue , then- Set value to ?
Call (toJSON, value, « key »).
- Set value to ?
- Let toJSON be ?
- If state.[[ReplacerFunction]]
is not
undefined , then- Set value to ?
Call (state.[[ReplacerFunction]], holder, « key, value »).
- Set value to ?
- If value
is an Object , then- If value has a [[NumberData]] internal slot, then
- Set value to ?
ToNumber (value).
- Set value to ?
- Else if value has a [[StringData]] internal slot, then
- Set value to ?
ToString (value).
- Set value to ?
- Else if value has a [[BooleanData]] internal slot, then
- Set value to value.[[BooleanData]].
- Else if value has a [[BigIntData]] internal slot, then
- Set value to value.[[BigIntData]].
- If value has a [[NumberData]] internal slot, then
- If value is
null , return"null" . - If value is
true , return"true" . - If value is
false , return"false" . - If value
is a String , returnQuoteJSONString (value). - If value
is a Number , then - If value
is a BigInt , throw aTypeError exception. - If value
is an Object andIsCallable (value) isfalse , then- Let isArray be ?
IsArray (value). - If isArray is
true , return ?SerializeJSONArray (state, value). - Return ?
SerializeJSONObject (state, value).
- Let isArray be ?
- Return
undefined .
25.5.2.3 QuoteJSONString ( value )
The abstract operation QuoteJSONString takes argument value (a String) and returns a
String.
It wraps value in 0x0022 (QUOTATION MARK) code units and escapes certain other code units
within it. This operation interprets value as a sequence of UTF-16 encoded code points, as
described in
- Let product be the String value consisting solely of the code unit 0x0022 (QUOTATION MARK).
- For each code point C of
StringToCodePoints (value), do- If C is listed in the “Code Point” column of
Table 76 , then- Set product to the
string-concatenation of product and the escape sequence for C as specified in the “Escape Sequence” column of the corresponding row.
- Set product to the
- Else if C has a numeric value less than 0x0020
(SPACE) or C has the same numeric value as a
leading surrogate ortrailing surrogate , then- Let unit be the code unit whose numeric value is the numeric value of C.
- Set product to the
string-concatenation of product andUnicodeEscape (unit).
- Else,
- Set product to the
string-concatenation of product andUTF16EncodeCodePoint (C).
- Set product to the
- If C is listed in the “Code Point” column of
- Set product to the
string-concatenation of product and the code unit 0x0022 (QUOTATION MARK). - Return product.
| Code Point | Unicode Character Name | Escape Sequence |
|---|---|---|
| U+0008 | BACKSPACE |
\b
|
| U+0009 | CHARACTER TABULATION |
\t
|
| U+000A | LINE FEED (LF) |
\n
|
| U+000C | FORM FEED (FF) |
\f
|
| U+000D | CARRIAGE RETURN (CR) |
\r
|
| U+0022 | QUOTATION MARK |
\"
|
| U+005C | REVERSE SOLIDUS |
\\
|
25.5.2.4 UnicodeEscape ( C )
The abstract operation UnicodeEscape takes argument C (a code unit) and returns a String. It represents C as a Unicode escape sequence. It performs the following steps when called:
- Let n be the numeric value of C.
Assert : n ≤ 0xFFFF.- Let hex be the String representation of n, formatted as a lowercase hexadecimal number.
- Return the
string-concatenation of the code unit 0x005C (REVERSE SOLIDUS),"u" , andStringPad (hex, 4,"0" ,start ).
25.5.2.5 SerializeJSONObject ( state, value )
The abstract operation SerializeJSONObject takes arguments state (a
- If state.[[Stack]]
contains
value, throw a
TypeError exception because the structure is cyclical. - Append value to state.[[Stack]].
- Let stepback be state.[[Indent]].
- Set state.[[Indent]] to
the
string-concatenation of state.[[Indent]] and state.[[Gap]]. - If state.[[PropertyList]]
is
not
undefined , then- Let K be state.[[PropertyList]].
- Else,
- Let K be ?
EnumerableOwnProperties (value,key ).
- Let K be ?
- Let partial be a new empty
List . - For each element P of K, do
- Let strP be ?
SerializeJSONProperty (state, P, value). - If strP is not
undefined , then- Let member be
QuoteJSONString (P). - Set member to the
string-concatenation of member and":" . - If state.[[Gap]]
is
not the empty String, then
- Set member to the
string-concatenation of member and the code unit 0x0020 (SPACE).
- Set member to the
- Set member to the
string-concatenation of member and strP. - Append member to partial.
- Let member be
- Let strP be ?
- If partial is empty, then
- Let final be
"{}" .
- Let final be
- Else,
- If state.[[Gap]] is
the
empty String, then
- Let properties be the String value formed by concatenating all the element Strings of partial with each adjacent pair of Strings separated with the code unit 0x002C (COMMA). A comma is not inserted either before the first String or after the last String.
- Let final be the
string-concatenation of"{" , properties, and"}" .
- Else,
- Let separator be the
string-concatenation of the code unit 0x002C (COMMA), the code unit 0x000A (LINE FEED), and state.[[Indent]]. - Let properties be the String value formed by concatenating all the element Strings of partial with each adjacent pair of Strings separated with separator. The separator String is not inserted either before the first String or after the last String.
- Let final be the
string-concatenation of"{" , the code unit 0x000A (LINE FEED), state.[[Indent]], properties, the code unit 0x000A (LINE FEED), stepback, and"}" .
- Let separator be the
- If state.[[Gap]] is
the
empty String, then
- Remove the last element of state.[[Stack]].
- Set state.[[Indent]] to stepback.
- Return final.
25.5.2.6 SerializeJSONArray ( state, value )
The abstract operation SerializeJSONArray takes arguments state (a
- If state.[[Stack]]
contains
value, throw a
TypeError exception because the structure is cyclical. - Append value to state.[[Stack]].
- Let stepback be state.[[Indent]].
- Set state.[[Indent]] to
the
string-concatenation of state.[[Indent]] and state.[[Gap]]. - Let partial be a new empty
List . - Let len be ?
LengthOfArrayLike (value). - Let index be 0.
- Repeat, while index < len,
- Let strP be ?
SerializeJSONProperty (state, !ToString (𝔽 (index)), value). - If strP is
undefined , then- Append
"null" to partial.
- Append
- Else,
- Append strP to partial.
- Set index to index + 1.
- Let strP be ?
- If partial is empty, then
- Let final be
"[]" .
- Let final be
- Else,
- If state.[[Gap]] is
the
empty String, then
- Let properties be the String value formed by concatenating all the element Strings of partial with each adjacent pair of Strings separated with the code unit 0x002C (COMMA). A comma is not inserted either before the first String or after the last String.
- Let final be the
string-concatenation of"[" , properties, and"]" .
- Else,
- Let separator be the
string-concatenation of the code unit 0x002C (COMMA), the code unit 0x000A (LINE FEED), and state.[[Indent]]. - Let properties be the String value formed by concatenating all the element Strings of partial with each adjacent pair of Strings separated with separator. The separator String is not inserted either before the first String or after the last String.
- Let final be the
string-concatenation of"[" , the code unit 0x000A (LINE FEED), state.[[Indent]], properties, the code unit 0x000A (LINE FEED), stepback, and"]" .
- Let separator be the
- If state.[[Gap]] is
the
empty String, then
- Remove the last element of state.[[Stack]].
- Set state.[[Indent]] to stepback.
- Return final.
The representation of arrays includes only the elements in the array.length (exclusive).
Properties
whose keys are not
25.5.3 JSON [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
26 Managing Memory
26.1 WeakRef Objects
A
26.1.1 The WeakRef Constructor
The WeakRef
- is %WeakRef%.
-
is the initial value of the
"WeakRef" property of theglobal object . -
creates and initializes a new WeakRef when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
-
may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specifiedWeakRefbehaviour must include asupercall to theWeakRefconstructor to create and initialize the subclass instance with the internal state necessary to support theWeakRef.prototypebuilt-in methods.
26.1.1.1 WeakRef ( target )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - If
CanBeHeldWeakly (target) isfalse , throw aTypeError exception. - Let weakRef be ?
OrdinaryCreateFromConstructor (NewTarget,"%WeakRef.prototype%" , « [[WeakRefTarget]] »). - Perform
AddToKeptObjects (target). - Set weakRef.[[WeakRefTarget]] to target.
- Return weakRef.
26.1.2 Properties of the WeakRef Constructor
The
-
has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
26.1.2.1 WeakRef.prototype
The initial value of WeakRef.prototype is the
This property has the attributes { [[Writable]]:
26.1.3 Properties of the WeakRef Prototype Object
The WeakRef prototype object:
- is %WeakRef.prototype%.
-
has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[WeakRefTarget]] internal slot.
26.1.3.1 WeakRef.prototype.constructor
The initial value of WeakRef.prototype.constructor is
This property has the attributes { [[Writable]]:
26.1.3.2 WeakRef.prototype.deref ( )
This method performs the following steps when called:
- Let weakRef be the
this value. - Perform ?
RequireInternalSlot (weakRef, [[WeakRefTarget]]). - Return
WeakRefDeref (weakRef).
If the
let target = { foo() {} };
let weakRef = new WeakRef(target);
// ... later ...
if (weakRef.deref()) {
weakRef.deref().foo();
}In the above example, if the first deref does not evaluate to
26.1.3.3 WeakRef.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
26.1.4 WeakRef Abstract Operations
26.1.4.1 WeakRefDeref ( weakRef )
The abstract operation WeakRefDeref takes argument weakRef (a
- Let target be weakRef.[[WeakRefTarget]].
- If target is not
empty , then- Perform
AddToKeptObjects (target). - Return target.
- Perform
- Return
undefined .
This abstract operation is defined separately from WeakRef.prototype.deref strictly to make it possible to succinctly define liveness.
26.1.5 Properties of WeakRef Instances
26.2 FinalizationRegistry Objects
A
26.2.1 The FinalizationRegistry Constructor
The FinalizationRegistry
- is %FinalizationRegistry%.
-
is the initial value of the
"FinalizationRegistry" property of theglobal object . -
creates and initializes a new FinalizationRegistry when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
-
may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specifiedFinalizationRegistrybehaviour must include asupercall to theFinalizationRegistryconstructor to create and initialize the subclass instance with the internal state necessary to support theFinalizationRegistry.prototypebuilt-in methods.
26.2.1.1 FinalizationRegistry ( cleanupCallback )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - If
IsCallable (cleanupCallback) isfalse , throw aTypeError exception. - Let finalizationRegistry be ?
OrdinaryCreateFromConstructor (NewTarget,"%FinalizationRegistry.prototype%" , « [[Realm]], [[CleanupCallback]], [[Cells]] »). - Let fn be the
active function object . - Set finalizationRegistry.[[Realm]] to fn.[[Realm]].
- Set finalizationRegistry.[[CleanupCallback]] to
HostMakeJobCallback (cleanupCallback). - Set finalizationRegistry.[[Cells]] to a new empty
List . - Return finalizationRegistry.
26.2.2 Properties of the FinalizationRegistry Constructor
The
-
has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
26.2.2.1 FinalizationRegistry.prototype
The initial value of FinalizationRegistry.prototype is the
This property has the attributes { [[Writable]]:
26.2.3 Properties of the FinalizationRegistry Prototype Object
The FinalizationRegistry prototype object:
- is %FinalizationRegistry.prototype%.
-
has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have [[Cells]] and [[CleanupCallback]] internal slots.
26.2.3.1 FinalizationRegistry.prototype.constructor
The initial value of FinalizationRegistry.prototype.constructor is
26.2.3.2 FinalizationRegistry.prototype.register ( target, heldValue [ , unregisterToken ] )
This method performs the following steps when called:
- Let finalizationRegistry be the
this value. - Perform ?
RequireInternalSlot (finalizationRegistry, [[Cells]]). - If
CanBeHeldWeakly (target) isfalse , throw aTypeError exception. - If
SameValue (target, heldValue) istrue , throw aTypeError exception. - If
CanBeHeldWeakly (unregisterToken) isfalse , then- If unregisterToken is not
undefined , throw aTypeError exception. - Set unregisterToken to
empty .
- If unregisterToken is not
- Let cell be the
Record { [[WeakRefTarget]]: target, [[HeldValue]]: heldValue, [[UnregisterToken]]: unregisterToken }. - Append cell to finalizationRegistry.[[Cells]].
- Return
undefined .
Based on the algorithms and definitions in this specification, cell.[[HeldValue]] is
26.2.3.3 FinalizationRegistry.prototype.unregister ( unregisterToken )
This method performs the following steps when called:
- Let finalizationRegistry be the
this value. - Perform ?
RequireInternalSlot (finalizationRegistry, [[Cells]]). - If
CanBeHeldWeakly (unregisterToken) isfalse , throw aTypeError exception. - Let removed be
false . - For each
Record { [[WeakRefTarget]], [[HeldValue]], [[UnregisterToken]] } cell of finalizationRegistry.[[Cells]], do- If cell.[[UnregisterToken]] is not
empty andSameValue (cell.[[UnregisterToken]], unregisterToken) istrue , then- Remove cell from finalizationRegistry.[[Cells]].
- Set removed to
true .
- If cell.[[UnregisterToken]] is not
- Return removed.
26.2.3.4 FinalizationRegistry.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
26.2.4 Properties of FinalizationRegistry Instances
27 Control Abstraction Objects
27.1 Iteration
27.1.1 Common Iteration Interfaces
An interface is a set of
27.1.1.1 The Iterable Interface
The Iterable interface includes the property described in
| Property | Value | Requirements |
|---|---|---|
@@iterator
|
a function that returns an Iterator object | The returned object must conform to the Iterator interface. |
27.1.1.2 The Iterator Interface
An object that implements the Iterator interface must include the property in
| Property | Value | Requirements |
|---|---|---|
|
|
a function that returns an IteratorResult object |
The returned object must conform to the IteratorResult interface. If a previous call
to
the next method of an Iterator has returned an IteratorResult
object
whose next method of that object should also return an IteratorResult
object whose |
Arguments may be passed to the next function but their interpretation and validity
is
dependent upon the target Iterator. The for-of statement and other common users of
Iterators do not pass any arguments, so Iterator objects that expect to be used in
such a manner must be prepared to deal with being called with no arguments.
| Property | Value | Requirements |
|---|---|---|
|
|
a function that returns an IteratorResult object |
The returned object must conform to the IteratorResult interface. Invoking this
method
notifies the Iterator object that the caller does not intend to make any more
next method calls to the Iterator. The returned IteratorResult
object
will typically have a return method. However, this requirement is not enforced.
|
|
|
a function that returns an IteratorResult object |
The returned object must conform to the IteratorResult interface. Invoking this
method
notifies the Iterator object that the caller has detected an error condition. The
argument may be used to identify the error condition and typically will be an exception
object.
A typical response is to throw the value passed as the argument. If the method
does
not throw, the returned IteratorResult object will typically have a
|
Typically callers of these methods should check for their existence before invoking them. Certain
ECMAScript language features including for-of, yield*, and
array destructuring call these methods after performing an existence check. Most ECMAScript
library
functions that accept Iterable objects as arguments also conditionally call them.
27.1.1.3 The AsyncIterable Interface
The AsyncIterable interface includes the properties described in
| Property | Value | Requirements |
|---|---|---|
@@asyncIterator |
a function that returns an AsyncIterator object | The returned object must conform to the AsyncIterator interface. |
27.1.1.4 The AsyncIterator Interface
An object that implements the AsyncIterator interface must include the properties in
| Property | Value | Requirements |
|---|---|---|
| a function that returns a promise for an IteratorResult object |
The returned promise, when fulfilled, must fulfill with an object that conforms to the
IteratorResult interface. If a previous call to the Additionally, the IteratorResult object that serves as a fulfillment value should
have
a |
Arguments may be passed to the next function but their interpretation and validity
is
dependent upon the target AsyncIterator. The
for-await-of statement and other common users of
AsyncIterators do not pass any arguments, so AsyncIterator objects that expect to
be
used in such a manner must be prepared to deal with being called with no arguments.
| Property | Value | Requirements |
|---|---|---|
| a function that returns a promise for an IteratorResult object |
The returned promise, when fulfilled, must fulfill with an object that conforms to the
IteratorResult interface. Invoking this method notifies the AsyncIterator
object
that the caller does not intend to make any more Additionally, the IteratorResult object that serves as a fulfillment value should
have
a |
|
| a function that returns a promise for an IteratorResult object |
The returned promise, when fulfilled, must fulfill with an object that conforms to the IteratorResult interface. Invoking this method notifies the AsyncIterator object that the caller has detected an error condition. The argument may be used to identify the error condition and typically will be an exception object. A typical response is to return a rejected promise which rejects with the value passed as the argument. If the returned promise is fulfilled, the IteratorResult fulfillment value will
typically have a |
Typically callers of these methods should check for their existence before invoking them. Certain
ECMAScript language features including for-await-of and
yield* call these methods after performing an existence check.
27.1.1.5 The IteratorResult Interface
The IteratorResult interface includes the properties listed in
| Property | Value | Requirements |
|---|---|---|
|
|
a Boolean |
This is the result status of an iterator next method call. If the end
of
the iterator was reached |
|
|
an |
If done is |
27.1.2 The %IteratorPrototype% Object
The %IteratorPrototype% object:
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object .
All objects defined in this specification that implement the Iterator interface also inherit from %IteratorPrototype%. ECMAScript code may also define objects that inherit from %IteratorPrototype%. The %IteratorPrototype% object provides a place where additional methods that are applicable to all iterator objects may be added.
The following expression is one way that ECMAScript code can access the %IteratorPrototype% object:
Object.getPrototypeOf(Object.getPrototypeOf([][Symbol.iterator]()))27.1.2.1 %IteratorPrototype% [ @@iterator ] ( )
This function performs the following steps when called:
- Return the
this value.
The value of the
27.1.3 The %AsyncIteratorPrototype% Object
The %AsyncIteratorPrototype% object:
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object .
All objects defined in this specification that implement the AsyncIterator interface also inherit from %AsyncIteratorPrototype%. ECMAScript code may also define objects that inherit from %AsyncIteratorPrototype%. The %AsyncIteratorPrototype% object provides a place where additional methods that are applicable to all async iterator objects may be added.
27.1.3.1 %AsyncIteratorPrototype% [ @@asyncIterator ] ( )
This function performs the following steps when called:
- Return the
this value.
The value of the
27.1.4 Async-from-Sync Iterator Objects
An Async-from-Sync Iterator object is an async iterator that adapts a specific synchronous iterator.
There
is not a named
27.1.4.1 CreateAsyncFromSyncIterator ( syncIteratorRecord )
The abstract operation CreateAsyncFromSyncIterator takes argument syncIteratorRecord (an
- Let asyncIterator be
OrdinaryObjectCreate (%AsyncFromSyncIteratorPrototype% , « [[SyncIteratorRecord]] »). - Set asyncIterator.[[SyncIteratorRecord]] to syncIteratorRecord.
- Let nextMethod be !
Get (asyncIterator,"next" ). - Let iteratorRecord be the
Iterator Record { [[Iterator]]: asyncIterator, [[NextMethod]]: nextMethod, [[Done]]:false }. - Return iteratorRecord.
27.1.4.2 The %AsyncFromSyncIteratorPrototype% Object
The %AsyncFromSyncIteratorPrototype% object:
- has properties that are inherited by all Async-from-Sync Iterator Objects.
- is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%AsyncIteratorPrototype% . - has the following properties:
27.1.4.2.1 %AsyncFromSyncIteratorPrototype%.next ( [ value ] )
- Let O be the
this value. Assert : Ois an Object that has a [[SyncIteratorRecord]] internal slot.- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let syncIteratorRecord be O.[[SyncIteratorRecord]].
- If value is present, then
- Let result be
Completion (IteratorNext (syncIteratorRecord, value)).
- Let result be
- Else,
- Let result be
Completion (IteratorNext (syncIteratorRecord)).
- Let result be
IfAbruptRejectPromise (result, promiseCapability).- Return
AsyncFromSyncIteratorContinuation (result, promiseCapability).
27.1.4.2.2 %AsyncFromSyncIteratorPrototype%.return ( [ value ] )
- Let O be the
this value. Assert : Ois an Object that has a [[SyncIteratorRecord]] internal slot.- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let syncIterator be O.[[SyncIteratorRecord]].[[Iterator]].
- Let return be
Completion (GetMethod (syncIterator,"return" )). IfAbruptRejectPromise (return, promiseCapability).- If return is
undefined , then- Let iterResult be
CreateIterResultObject (value,true ). - Perform !
Call (promiseCapability.[[Resolve]],undefined , « iterResult »). - Return promiseCapability.[[Promise]].
- Let iterResult be
- If value is present, then
- Let result be
Completion (Call (return, syncIterator, « value »)).
- Let result be
- Else,
- Let result be
Completion (Call (return, syncIterator)).
- Let result be
IfAbruptRejectPromise (result, promiseCapability).- If result
is not an Object , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - Return promiseCapability.[[Promise]].
- Perform !
- Return
AsyncFromSyncIteratorContinuation (result, promiseCapability).
27.1.4.2.3 %AsyncFromSyncIteratorPrototype%.throw ( [ value ] )
- Let O be the
this value. Assert : Ois an Object that has a [[SyncIteratorRecord]] internal slot.- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let syncIterator be O.[[SyncIteratorRecord]].[[Iterator]].
- Let throw be
Completion (GetMethod (syncIterator,"throw" )). IfAbruptRejectPromise (throw, promiseCapability).- If throw is
undefined , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « value »). - Return promiseCapability.[[Promise]].
- Perform !
- If value is present, then
- Let result be
Completion (Call (throw, syncIterator, « value »)).
- Let result be
- Else,
- Let result be
Completion (Call (throw, syncIterator)).
- Let result be
IfAbruptRejectPromise (result, promiseCapability).- If result
is not an Object , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - Return promiseCapability.[[Promise]].
- Perform !
- Return
AsyncFromSyncIteratorContinuation (result, promiseCapability).
27.1.4.3 Properties of Async-from-Sync Iterator Instances
Async-from-Sync Iterator instances are
| Internal Slot | Type | Description |
|---|---|---|
| [[SyncIteratorRecord]] |
an |
Represents the original synchronous iterator which is being adapted. |
27.1.4.4 AsyncFromSyncIteratorContinuation ( result, promiseCapability )
The abstract operation AsyncFromSyncIteratorContinuation takes arguments result (an
Object)
and promiseCapability (a
- NOTE: Because promiseCapability is derived from
the
intrinsic
%Promise% , the calls to promiseCapability.[[Reject]] entailed by the useIfAbruptRejectPromise below are guaranteed not to throw. - Let done be
Completion (IteratorComplete (result)). IfAbruptRejectPromise (done, promiseCapability).- Let value be
Completion (IteratorValue (result)). IfAbruptRejectPromise (value, promiseCapability).- Let valueWrapper be
Completion (PromiseResolve (%Promise% , value)). IfAbruptRejectPromise (valueWrapper, promiseCapability).- Let unwrap be a new
Abstract Closure with parameters (v) that captures done and performs the following steps when called:- Return
CreateIterResultObject (v, done).
- Return
- Let onFulfilled be
CreateBuiltinFunction (unwrap, 1,"" , « »). - NOTE: onFulfilled is used when processing the
"value" property of an IteratorResult object in order to wait for its value if it is a promise and re-package the result in a new "unwrapped" IteratorResult object. - Perform
PerformPromiseThen (valueWrapper, onFulfilled,undefined , promiseCapability). - Return promiseCapability.[[Promise]].
27.2 Promise Objects
A Promise is an object that is used as a placeholder for the eventual results of a deferred (and possibly asynchronous) computation.
Any Promise is in one of three mutually exclusive states: fulfilled, rejected, and pending:
-
A promise
pis fulfilled ifp.then(f, r)will immediately enqueue aJob to call the functionf. -
A promise
pis rejected ifp.then(f, r)will immediately enqueue aJob to call the functionr. - A promise is pending if it is neither fulfilled nor rejected.
A promise is said to be settled if it is not pending, i.e. if it is either fulfilled or rejected.
A promise is resolved if it is settled or if it has been “locked in” to match the state of another promise. Attempting to resolve or reject a resolved promise has no effect. A promise is unresolved if it is not resolved. An unresolved promise is always in the pending state. A resolved promise may be pending, fulfilled or rejected.
27.2.1 Promise Abstract Operations
27.2.1.1 PromiseCapability Records
A PromiseCapability Record is a
PromiseCapability Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Promise]] | an Object | An object that is usable as a promise. |
| [[Resolve]] |
a |
The function that is used to resolve the given promise. |
| [[Reject]] |
a |
The function that is used to reject the given promise. |
27.2.1.1.1 IfAbruptRejectPromise ( value, capability )
IfAbruptRejectPromise is a shorthand for a sequence of algorithm steps that use a
IfAbruptRejectPromise (value, capability).
means the same thing as:
Assert : value is aCompletion Record .- If value is an
abrupt completion , then- Perform ?
Call (capability.[[Reject]],undefined , « value.[[Value]] »). - Return capability.[[Promise]].
- Perform ?
- Else,
- Set value to ! value.
27.2.1.2 PromiseReaction Records
A PromiseReaction Record is a
PromiseReaction Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Capability]] |
a |
The capabilities of the promise for which this record provides a reaction handler. |
| [[Type]] |
|
The [[Type]] is used when [[Handler]] is
|
| [[Handler]] |
a |
The function that should be applied to the incoming value, and whose return value will
govern
what happens to the derived promise. If [[Handler]] is
|
27.2.1.3 CreateResolvingFunctions ( promise )
The abstract operation CreateResolvingFunctions takes argument promise (a Promise) and
returns
a
- Let alreadyResolved be the
Record { [[Value]]:false }. - Let stepsResolve be the algorithm steps defined in
Promise Resolve Functions . - Let lengthResolve be the number of non-optional
parameters of the function definition in
Promise Resolve Functions . - Let resolve be
CreateBuiltinFunction (stepsResolve, lengthResolve,"" , « [[Promise]], [[AlreadyResolved]] »). - Set resolve.[[Promise]] to promise.
- Set resolve.[[AlreadyResolved]] to alreadyResolved.
- Let stepsReject be the algorithm steps defined in
Promise Reject Functions . - Let lengthReject be the number of non-optional
parameters of the function definition in
Promise Reject Functions . - Let reject be
CreateBuiltinFunction (stepsReject, lengthReject,"" , « [[Promise]], [[AlreadyResolved]] »). - Set reject.[[Promise]] to promise.
- Set reject.[[AlreadyResolved]] to alreadyResolved.
- Return the
Record { [[Resolve]]: resolve, [[Reject]]: reject }.
27.2.1.3.1 Promise Reject Functions
A promise reject function is an anonymous built-in function that has [[Promise]] and [[AlreadyResolved]] internal slots.
When a promise reject function is called with argument reason, the following steps are taken:
- Let F be the
active function object . Assert : F has a [[Promise]] internal slot whose valueis an Object .- Let promise be F.[[Promise]].
- Let alreadyResolved be F.[[AlreadyResolved]].
- If alreadyResolved.[[Value]] is
true , returnundefined . - Set alreadyResolved.[[Value]] to
true . - Perform
RejectPromise (promise, reason). - Return
undefined .
The
27.2.1.3.2 Promise Resolve Functions
A promise resolve function is an anonymous built-in function that has [[Promise]] and [[AlreadyResolved]] internal slots.
When a promise resolve function is called with argument resolution, the following steps are taken:
- Let F be the
active function object . Assert : F has a [[Promise]] internal slot whose valueis an Object .- Let promise be F.[[Promise]].
- Let alreadyResolved be F.[[AlreadyResolved]].
- If alreadyResolved.[[Value]] is
true , returnundefined . - Set alreadyResolved.[[Value]] to
true . - If
SameValue (resolution, promise) istrue , then- Let selfResolutionError be a newly created
TypeError object. - Perform
RejectPromise (promise, selfResolutionError). - Return
undefined .
- Let selfResolutionError be a newly created
- If resolution
is not an Object , then- Perform
FulfillPromise (promise, resolution). - Return
undefined .
- Perform
- Let then be
Completion (Get (resolution,"then" )). - If then is an
abrupt completion , then- Perform
RejectPromise (promise, then.[[Value]]). - Return
undefined .
- Perform
- Let thenAction be then.[[Value]].
- If
IsCallable (thenAction) isfalse , then- Perform
FulfillPromise (promise, resolution). - Return
undefined .
- Perform
- Let thenJobCallback be
HostMakeJobCallback (thenAction). - Let job be
NewPromiseResolveThenableJob (promise, resolution, thenJobCallback). - Perform
HostEnqueuePromiseJob (job.[[Job]], job.[[Realm]]). - Return
undefined .
The
27.2.1.4 FulfillPromise ( promise, value )
The abstract operation FulfillPromise takes arguments promise (a Promise) and
value
(an
Assert : The value of promise.[[PromiseState]] ispending .- Let reactions be promise.[[PromiseFulfillReactions]].
- Set promise.[[PromiseResult]] to value.
- Set promise.[[PromiseFulfillReactions]] to
undefined . - Set promise.[[PromiseRejectReactions]] to
undefined . - Set promise.[[PromiseState]]
to
fulfilled . - Perform
TriggerPromiseReactions (reactions, value). - Return
unused .
27.2.1.5 NewPromiseCapability ( C )
The abstract operation NewPromiseCapability takes argument C (an resolve and reject functions. The promise plus the
resolve and reject functions are used to initialize a new
- If
IsConstructor (C) isfalse , throw aTypeError exception. - NOTE: C is assumed to be a
constructor function that supports the parameter conventions of the Promiseconstructor (see27.2.3.1 ). - Let resolvingFunctions be the
Record { [[Resolve]]:undefined , [[Reject]]:undefined }. - Let executorClosure be a new
Abstract Closure with parameters (resolve, reject) that captures resolvingFunctions and performs the following steps when called:- If resolvingFunctions.[[Resolve]] is not
undefined , throw aTypeError exception. - If resolvingFunctions.[[Reject]] is not
undefined , throw aTypeError exception. - Set resolvingFunctions.[[Resolve]] to resolve.
- Set resolvingFunctions.[[Reject]] to reject.
- Return
undefined .
- If resolvingFunctions.[[Resolve]] is not
- Let executor be
CreateBuiltinFunction (executorClosure, 2,"" , « »). - Let promise be ?
Construct (C, « executor »). - If
IsCallable (resolvingFunctions.[[Resolve]]) isfalse , throw aTypeError exception. - If
IsCallable (resolvingFunctions.[[Reject]]) isfalse , throw aTypeError exception. - Return the
PromiseCapability Record { [[Promise]]: promise, [[Resolve]]: resolvingFunctions.[[Resolve]], [[Reject]]: resolvingFunctions.[[Reject]] }.
This abstract operation supports Promise subclassing, as it is generic on any
27.2.1.6 IsPromise ( x )
The abstract operation IsPromise takes argument x (an
- If x
is not an Object , returnfalse . - If x does not have a [[PromiseState]] internal slot, return
false . - Return
true .
27.2.1.7 RejectPromise ( promise, reason )
The abstract operation RejectPromise takes arguments promise (a Promise) and
reason
(an
Assert : The value of promise.[[PromiseState]] ispending .- Let reactions be promise.[[PromiseRejectReactions]].
- Set promise.[[PromiseResult]] to reason.
- Set promise.[[PromiseFulfillReactions]] to
undefined . - Set promise.[[PromiseRejectReactions]] to
undefined . - Set promise.[[PromiseState]]
to
rejected . - If promise.[[PromiseIsHandled]] is
false , performHostPromiseRejectionTracker (promise,"reject" ). - Perform
TriggerPromiseReactions (reactions, reason). - Return
unused .
27.2.1.8 TriggerPromiseReactions ( reactions, argument )
The abstract operation TriggerPromiseReactions takes arguments reactions (a
- For each element reaction of reactions,
do
- Let job be
NewPromiseReactionJob (reaction, argument). - Perform
HostEnqueuePromiseJob (job.[[Job]], job.[[Realm]]).
- Let job be
- Return
unused .
27.2.1.9 HostPromiseRejectionTracker ( promise, operation )
The
The default implementation of HostPromiseRejectionTracker is to return
HostPromiseRejectionTracker is called in two scenarios:
- When a promise is rejected without any handlers, it is called with its operation
argument set to
"reject" . - When a handler is added to a rejected promise for the first time, it is called with its
operation argument set to
"handle" .
A typical implementation of HostPromiseRejectionTracker might try to notify developers of unhandled rejections, while also being careful to notify them if such previous notifications are later invalidated by new handlers being attached.
If operation is
27.2.2 Promise Jobs
27.2.2.1 NewPromiseReactionJob ( reaction, argument )
The abstract operation NewPromiseReactionJob takes arguments reaction (a
- Let job be a new
Job Abstract Closure with no parameters that captures reaction and argument and performs the following steps when called:- Let promiseCapability be reaction.[[Capability]].
- Let type be reaction.[[Type]].
- Let handler be reaction.[[Handler]].
- If handler is
empty , then- If type is
fulfill , then- Let handlerResult be
NormalCompletion (argument).
- Let handlerResult be
- Else,
Assert : type isreject .- Let handlerResult be
ThrowCompletion (argument).
- If type is
- Else,
- Let handlerResult be
Completion (HostCallJobCallback (handler,undefined , « argument »)).
- Let handlerResult be
- If promiseCapability is
undefined , thenAssert : handlerResult is not anabrupt completion .- Return
empty .
Assert : promiseCapability is aPromiseCapability Record .- If handlerResult is an
abrupt completion , then- Return ?
Call (promiseCapability.[[Reject]],undefined , « handlerResult.[[Value]] »).
- Return ?
- Else,
- Return ?
Call (promiseCapability.[[Resolve]],undefined , « handlerResult.[[Value]] »).
- Return ?
- Let handlerRealm be
null . - If reaction.[[Handler]]
is
not
empty , then- Let getHandlerRealmResult be
Completion (GetFunctionRealm (reaction.[[Handler]].[[Callback]])). - If getHandlerRealmResult is a
normal completion , set handlerRealm to getHandlerRealmResult.[[Value]]. - Else, set handlerRealm to
the current Realm Record . - NOTE: handlerRealm is never
null unless the handler isundefined . When the handler is a revoked Proxy and no ECMAScript code runs, handlerRealm is used to create error objects.
- Let getHandlerRealmResult be
- Return the
Record { [[Job]]: job, [[Realm]]: handlerRealm }.
27.2.2.2 NewPromiseResolveThenableJob ( promiseToResolve, thenable, then )
The abstract operation NewPromiseResolveThenableJob takes arguments promiseToResolve (a
Promise), thenable (an Object), and then (a
- Let job be a new
Job Abstract Closure with no parameters that captures promiseToResolve, thenable, and then and performs the following steps when called:- Let resolvingFunctions be
CreateResolvingFunctions (promiseToResolve). - Let thenCallResult be
Completion (HostCallJobCallback (then, thenable, « resolvingFunctions.[[Resolve]], resolvingFunctions.[[Reject]] »)). - If thenCallResult is an
abrupt completion , then- Return ?
Call (resolvingFunctions.[[Reject]],undefined , « thenCallResult.[[Value]] »).
- Return ?
- Return ? thenCallResult.
- Let resolvingFunctions be
- Let getThenRealmResult be
Completion (GetFunctionRealm (then.[[Callback]])). - If getThenRealmResult is a
normal completion , let thenRealm be getThenRealmResult.[[Value]]. - Else, let thenRealm be
the current Realm Record . - NOTE: thenRealm is never
null . When then.[[Callback]] is a revoked Proxy and no code runs, thenRealm is used to create error objects. - Return the
Record { [[Job]]: job, [[Realm]]: thenRealm }.
27.2.3 The Promise Constructor
The Promise
- is %Promise%.
- is the initial value of the
"Promise" property of theglobal object . - creates and initializes a new Promise when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Promise behaviour must include asupercall to the Promiseconstructor to create and initialize the subclass instance with the internal state necessary to support thePromiseandPromise.prototypebuilt-in methods.
27.2.3.1 Promise ( executor )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - If
IsCallable (executor) isfalse , throw aTypeError exception. - Let promise be ?
OrdinaryCreateFromConstructor (NewTarget,"%Promise.prototype%" , « [[PromiseState]], [[PromiseResult]], [[PromiseFulfillReactions]], [[PromiseRejectReactions]], [[PromiseIsHandled]] »). - Set promise.[[PromiseState]]
to
pending . - Set promise.[[PromiseFulfillReactions]] to a new empty
List . - Set promise.[[PromiseRejectReactions]] to a new empty
List . - Set promise.[[PromiseIsHandled]] to
false . - Let resolvingFunctions be
CreateResolvingFunctions (promise). - Let completion be
Completion (Call (executor,undefined , « resolvingFunctions.[[Resolve]], resolvingFunctions.[[Reject]] »)). - If completion is an
abrupt completion , then- Perform ?
Call (resolvingFunctions.[[Reject]],undefined , « completion.[[Value]] »).
- Perform ?
- Return promise.
The executor argument must be a
The resolve function that is passed to an executor function accepts a single argument. The executor code may eventually call the resolve function to indicate that it wishes to resolve the associated Promise. The argument passed to the resolve function represents the eventual value of the deferred action and can be either the actual fulfillment value or another promise which will provide the value if it is fulfilled.
The reject function that is passed to an executor function accepts a single argument. The executor code may eventually call the reject function to indicate that the associated Promise is rejected and will never be fulfilled. The argument passed to the reject function is used as the rejection value of the promise. Typically it will be an Error object.
The resolve and reject functions passed to an executor function by the Promise
27.2.4 Properties of the Promise Constructor
The Promise
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
27.2.4.1 Promise.all ( iterable )
This function returns a new promise which is fulfilled with an array of fulfillment values for the passed promises, or rejects with the reason of the first passed promise that rejects. It resolves all elements of the passed iterable to promises as it runs this algorithm.
- Let C be the
this value. - Let promiseCapability be ?
NewPromiseCapability (C). - Let promiseResolve be
Completion (GetPromiseResolve (C)). IfAbruptRejectPromise (promiseResolve, promiseCapability).- Let iteratorRecord be
Completion (GetIterator (iterable,sync )). IfAbruptRejectPromise (iteratorRecord, promiseCapability).- Let result be
Completion (PerformPromiseAll (iteratorRecord, C, promiseCapability, promiseResolve)). - If result is an
abrupt completion , then- If iteratorRecord.[[Done]] is
false , set result toCompletion (IteratorClose (iteratorRecord, result)). IfAbruptRejectPromise (result, promiseCapability).
- If iteratorRecord.[[Done]] is
- Return ? result.
This function requires its
27.2.4.1.1 GetPromiseResolve ( promiseConstructor )
The abstract operation GetPromiseResolve takes argument promiseConstructor (a
- Let promiseResolve be ?
Get (promiseConstructor,"resolve" ). - If
IsCallable (promiseResolve) isfalse , throw aTypeError exception. - Return promiseResolve.
27.2.4.1.2 PerformPromiseAll ( iteratorRecord, constructor, resultCapability, promiseResolve )
The abstract operation PerformPromiseAll takes arguments iteratorRecord (an
- Let values be a new empty
List . - Let remainingElementsCount be the
Record { [[Value]]: 1 }. - Let index be 0.
- Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , then- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0, then
- Let valuesArray be
CreateArrayFromList (values). - Perform ?
Call (resultCapability.[[Resolve]],undefined , « valuesArray »).
- Let valuesArray be
- Return resultCapability.[[Promise]].
- Append
undefined to values. - Let nextPromise be ?
Call (promiseResolve, constructor, « next »). - Let steps be the algorithm steps defined in
Promise.allResolve Element Functions - Let length be the number of non-optional
parameters of the function definition in
Promise.allResolve Element Functions - Let onFulfilled be
CreateBuiltinFunction (steps, length,"" , « [[AlreadyCalled]], [[Index]], [[Values]], [[Capability]], [[RemainingElements]] »). - Set onFulfilled.[[AlreadyCalled]] to
false . - Set onFulfilled.[[Index]] to index.
- Set onFulfilled.[[Values]] to values.
- Set onFulfilled.[[Capability]] to resultCapability.
- Set onFulfilled.[[RemainingElements]] to remainingElementsCount.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] + 1.
- Perform ?
Invoke (nextPromise,"then" , « onFulfilled, resultCapability.[[Reject]] »). - Set index to index + 1.
- Let next be ?
27.2.4.1.3 Promise.all Resolve Element Functions
A Promise.all resolve element function is an anonymous built-in function that is used
to
resolve a specific Promise.all element. Each Promise.all resolve element
function has [[Index]], [[Values]], [[Capability]], [[RemainingElements]], and [[AlreadyCalled]] internal slots.
When a Promise.all resolve element function is called with argument x, the
following steps are taken:
- Let F be the
active function object . - If F.[[AlreadyCalled]]
is
true , returnundefined . - Set F.[[AlreadyCalled]]
to
true . - Let index be F.[[Index]].
- Let values be F.[[Values]].
- Let promiseCapability be F.[[Capability]].
- Let remainingElementsCount be F.[[RemainingElements]].
- Set values[index] to x.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0, then
- Let valuesArray be
CreateArrayFromList (values). - Return ?
Call (promiseCapability.[[Resolve]],undefined , « valuesArray »).
- Let valuesArray be
- Return
undefined .
The Promise.all resolve element function is
27.2.4.2 Promise.allSettled ( iterable )
This function returns a promise that is fulfilled with an array of promise state snapshots, but only after all the original promises have settled, i.e. become either fulfilled or rejected. It resolves all elements of the passed iterable to promises as it runs this algorithm.
- Let C be the
this value. - Let promiseCapability be ?
NewPromiseCapability (C). - Let promiseResolve be
Completion (GetPromiseResolve (C)). IfAbruptRejectPromise (promiseResolve, promiseCapability).- Let iteratorRecord be
Completion (GetIterator (iterable,sync )). IfAbruptRejectPromise (iteratorRecord, promiseCapability).- Let result be
Completion (PerformPromiseAllSettled (iteratorRecord, C, promiseCapability, promiseResolve)). - If result is an
abrupt completion , then- If iteratorRecord.[[Done]] is
false , set result toCompletion (IteratorClose (iteratorRecord, result)). IfAbruptRejectPromise (result, promiseCapability).
- If iteratorRecord.[[Done]] is
- Return ? result.
This function requires its
27.2.4.2.1 PerformPromiseAllSettled ( iteratorRecord, constructor, resultCapability, promiseResolve )
The abstract operation PerformPromiseAllSettled takes arguments iteratorRecord (an
- Let values be a new empty
List . - Let remainingElementsCount be the
Record { [[Value]]: 1 }. - Let index be 0.
- Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , then- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0, then
- Let valuesArray be
CreateArrayFromList (values). - Perform ?
Call (resultCapability.[[Resolve]],undefined , « valuesArray »).
- Let valuesArray be
- Return resultCapability.[[Promise]].
- Append
undefined to values. - Let nextPromise be ?
Call (promiseResolve, constructor, « next »). - Let stepsFulfilled be the algorithm steps
defined in
Promise.allSettledResolve Element Functions - Let lengthFulfilled be the number of
non-optional parameters of the function definition in
Promise.allSettledResolve Element Functions - Let onFulfilled be
CreateBuiltinFunction (stepsFulfilled, lengthFulfilled,"" , « [[AlreadyCalled]], [[Index]], [[Values]], [[Capability]], [[RemainingElements]] »). - Let alreadyCalled be the
Record { [[Value]]:false }. - Set onFulfilled.[[AlreadyCalled]] to alreadyCalled.
- Set onFulfilled.[[Index]] to index.
- Set onFulfilled.[[Values]] to values.
- Set onFulfilled.[[Capability]] to resultCapability.
- Set onFulfilled.[[RemainingElements]] to remainingElementsCount.
- Let stepsRejected be the algorithm steps
defined
in
Promise.allSettledReject Element Functions - Let lengthRejected be the number of
non-optional
parameters of the function definition in
Promise.allSettledReject Element Functions - Let onRejected be
CreateBuiltinFunction (stepsRejected, lengthRejected,"" , « [[AlreadyCalled]], [[Index]], [[Values]], [[Capability]], [[RemainingElements]] »). - Set onRejected.[[AlreadyCalled]] to alreadyCalled.
- Set onRejected.[[Index]] to index.
- Set onRejected.[[Values]] to values.
- Set onRejected.[[Capability]] to resultCapability.
- Set onRejected.[[RemainingElements]] to remainingElementsCount.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] + 1.
- Perform ?
Invoke (nextPromise,"then" , « onFulfilled, onRejected »). - Set index to index + 1.
- Let next be ?
27.2.4.2.2 Promise.allSettled Resolve Element Functions
A Promise.allSettled resolve element function is an anonymous built-in function that
is
used to resolve a specific Promise.allSettled element. Each
Promise.allSettled
resolve element function has [[Index]], [[Values]],
[[Capability]], [[RemainingElements]], and [[AlreadyCalled]] internal slots.
When a Promise.allSettled resolve element function is called with argument
x,
the following steps are taken:
- Let F be the
active function object . - Let alreadyCalled be F.[[AlreadyCalled]].
- If alreadyCalled.[[Value]]
is
true , returnundefined . - Set alreadyCalled.[[Value]]
to
true . - Let index be F.[[Index]].
- Let values be F.[[Values]].
- Let promiseCapability be F.[[Capability]].
- Let remainingElementsCount be F.[[RemainingElements]].
- Let obj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (obj,"status" ,"fulfilled" ). - Perform !
CreateDataPropertyOrThrow (obj,"value" , x). - Set values[index] to obj.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0, then
- Let valuesArray be
CreateArrayFromList (values). - Return ?
Call (promiseCapability.[[Resolve]],undefined , « valuesArray »).
- Let valuesArray be
- Return
undefined .
The Promise.allSettled resolve element
function
is
27.2.4.2.3 Promise.allSettled Reject Element Functions
A Promise.allSettled reject element function is an anonymous built-in function that is
used to reject a specific Promise.allSettled element. Each
Promise.allSettled
reject element function has [[Index]], [[Values]],
[[Capability]], [[RemainingElements]], and [[AlreadyCalled]] internal slots.
When a Promise.allSettled reject element function is called with argument
x,
the following steps are taken:
- Let F be the
active function object . - Let alreadyCalled be F.[[AlreadyCalled]].
- If alreadyCalled.[[Value]]
is
true , returnundefined . - Set alreadyCalled.[[Value]]
to
true . - Let index be F.[[Index]].
- Let values be F.[[Values]].
- Let promiseCapability be F.[[Capability]].
- Let remainingElementsCount be F.[[RemainingElements]].
- Let obj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (obj,"status" ,"rejected" ). - Perform !
CreateDataPropertyOrThrow (obj,"reason" , x). - Set values[index] to obj.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0, then
- Let valuesArray be
CreateArrayFromList (values). - Return ?
Call (promiseCapability.[[Resolve]],undefined , « valuesArray »).
- Let valuesArray be
- Return
undefined .
The Promise.allSettled reject element
function
is
27.2.4.3 Promise.any ( iterable )
This function returns a promise that is fulfilled by the first given promise to be fulfilled, or
rejected
with an AggregateError holding the rejection reasons if all of the given promises are
rejected. It resolves all elements of the passed iterable to promises as it runs this algorithm.
- Let C be the
this value. - Let promiseCapability be ?
NewPromiseCapability (C). - Let promiseResolve be
Completion (GetPromiseResolve (C)). IfAbruptRejectPromise (promiseResolve, promiseCapability).- Let iteratorRecord be
Completion (GetIterator (iterable,sync )). IfAbruptRejectPromise (iteratorRecord, promiseCapability).- Let result be
Completion (PerformPromiseAny (iteratorRecord, C, promiseCapability, promiseResolve)). - If result is an
abrupt completion , then- If iteratorRecord.[[Done]] is
false , set result toCompletion (IteratorClose (iteratorRecord, result)). IfAbruptRejectPromise (result, promiseCapability).
- If iteratorRecord.[[Done]] is
- Return ? result.
This function requires its Promise
27.2.4.3.1 PerformPromiseAny ( iteratorRecord, constructor, resultCapability, promiseResolve )
The abstract operation PerformPromiseAny takes arguments iteratorRecord (an
- Let errors be a new empty
List . - Let remainingElementsCount be the
Record { [[Value]]: 1 }. - Let index be 0.
- Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , then- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0, then
- Let error be a newly created
AggregateError object. - Perform !
DefinePropertyOrThrow (error,"errors" , PropertyDescriptor { [[Configurable]]:true , [[Enumerable]]:false , [[Writable]]:true , [[Value]]:CreateArrayFromList (errors) }). - Return
ThrowCompletion (error).
- Let error be a newly created
- Return resultCapability.[[Promise]].
- Append
undefined to errors. - Let nextPromise be ?
Call (promiseResolve, constructor, « next »). - Let stepsRejected be the algorithm steps
defined
in
Promise.anyReject Element Functions - Let lengthRejected be the number of
non-optional
parameters of the function definition in
Promise.anyReject Element Functions - Let onRejected be
CreateBuiltinFunction (stepsRejected, lengthRejected,"" , « [[AlreadyCalled]], [[Index]], [[Errors]], [[Capability]], [[RemainingElements]] »). - Set onRejected.[[AlreadyCalled]] to
false . - Set onRejected.[[Index]] to index.
- Set onRejected.[[Errors]] to errors.
- Set onRejected.[[Capability]] to resultCapability.
- Set onRejected.[[RemainingElements]] to remainingElementsCount.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] + 1.
- Perform ?
Invoke (nextPromise,"then" , « resultCapability.[[Resolve]], onRejected »). - Set index to index + 1.
- Let next be ?
27.2.4.3.2 Promise.any Reject Element Functions
A Promise.any reject element function is an anonymous built-in function that is used
to
reject a specific Promise.any element. Each Promise.any reject element
function has [[Index]], [[Errors]], [[Capability]], [[RemainingElements]], and [[AlreadyCalled]] internal slots.
When a Promise.any reject element function is called with argument x, the
following steps are taken:
- Let F be the
active function object . - If F.[[AlreadyCalled]]
is
true , returnundefined . - Set F.[[AlreadyCalled]]
to
true . - Let index be F.[[Index]].
- Let errors be F.[[Errors]].
- Let promiseCapability be F.[[Capability]].
- Let remainingElementsCount be F.[[RemainingElements]].
- Set errors[index] to x.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0, then
- Let error be a newly created
AggregateError object. - Perform !
DefinePropertyOrThrow (error,"errors" , PropertyDescriptor { [[Configurable]]:true , [[Enumerable]]:false , [[Writable]]:true , [[Value]]:CreateArrayFromList (errors) }). - Return ?
Call (promiseCapability.[[Reject]],undefined , « error »).
- Let error be a newly created
- Return
undefined .
The Promise.any reject element function is
27.2.4.4 Promise.prototype
The initial value of Promise.prototype is the
This property has the attributes { [[Writable]]:
27.2.4.5 Promise.race ( iterable )
This function returns a new promise which is settled in the same way as the first passed promise to settle. It resolves all elements of the passed iterable to promises as it runs this algorithm.
- Let C be the
this value. - Let promiseCapability be ?
NewPromiseCapability (C). - Let promiseResolve be
Completion (GetPromiseResolve (C)). IfAbruptRejectPromise (promiseResolve, promiseCapability).- Let iteratorRecord be
Completion (GetIterator (iterable,sync )). IfAbruptRejectPromise (iteratorRecord, promiseCapability).- Let result be
Completion (PerformPromiseRace (iteratorRecord, C, promiseCapability, promiseResolve)). - If result is an
abrupt completion , then- If iteratorRecord.[[Done]] is
false , set result toCompletion (IteratorClose (iteratorRecord, result)). IfAbruptRejectPromise (result, promiseCapability).
- If iteratorRecord.[[Done]] is
- Return ? result.
If the iterable argument yields no values or if none of the promises yielded by iterable ever settle, then the pending promise returned by this method will never be settled.
This function expects its resolve method.
27.2.4.5.1 PerformPromiseRace ( iteratorRecord, constructor, resultCapability, promiseResolve )
The abstract operation PerformPromiseRace takes arguments iteratorRecord (an
- Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , then- Return resultCapability.[[Promise]].
- Let nextPromise be ?
Call (promiseResolve, constructor, « next »). - Perform ?
Invoke (nextPromise,"then" , « resultCapability.[[Resolve]], resultCapability.[[Reject]] »).
- Let next be ?
27.2.4.6 Promise.reject ( r )
This function returns a new promise rejected with the passed argument.
- Let C be the
this value. - Let promiseCapability be ?
NewPromiseCapability (C). - Perform ?
Call (promiseCapability.[[Reject]],undefined , « r »). - Return promiseCapability.[[Promise]].
This function expects its
27.2.4.7 Promise.resolve ( x )
This function returns either a new promise resolved with the passed argument, or the argument itself
if
the argument is a promise produced by this
- Let C be the
this value. - If C
is not an Object , throw aTypeError exception. - Return ?
PromiseResolve (C, x).
This function expects its
27.2.4.7.1 PromiseResolve ( C, x )
The abstract operation PromiseResolve takes arguments C (a
- If
IsPromise (x) istrue , then - Let promiseCapability be ?
NewPromiseCapability (C). - Perform ?
Call (promiseCapability.[[Resolve]],undefined , « x »). - Return promiseCapability.[[Promise]].
27.2.4.8 Promise.withResolvers ( )
This function returns an object with three properties: a new promise together with the
resolve and reject functions associated with it.
- Let C be the
this value. - Let promiseCapability be ?
NewPromiseCapability (C). - Let obj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (obj,"promise" , promiseCapability.[[Promise]]). - Perform !
CreateDataPropertyOrThrow (obj,"resolve" , promiseCapability.[[Resolve]]). - Perform !
CreateDataPropertyOrThrow (obj,"reject" , promiseCapability.[[Reject]]). - Return obj.
27.2.4.9 get Promise [ @@species ]
Promise[@@species] is an
- Return the
this value.
The value of the
Promise prototype methods normally use their
27.2.5 Properties of the Promise Prototype Object
The Promise prototype object:
- is %Promise.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[PromiseState]] internal slot or any of the other internal slots of Promise instances.
27.2.5.1 Promise.prototype.catch ( onRejected )
This method performs the following steps when called:
- Let promise be the
this value. - Return ?
Invoke (promise,"then" , «undefined , onRejected »).
27.2.5.2 Promise.prototype.constructor
The initial value of Promise.prototype.constructor is
27.2.5.3 Promise.prototype.finally ( onFinally )
This method performs the following steps when called:
- Let promise be the
this value. - If promise
is not an Object , throw aTypeError exception. - Let C be ?
SpeciesConstructor (promise,%Promise% ). Assert :IsConstructor (C) istrue .- If
IsCallable (onFinally) isfalse , then- Let thenFinally be onFinally.
- Let catchFinally be onFinally.
- Else,
- Let thenFinallyClosure be a new
Abstract Closure with parameters (value) that captures onFinally and C and performs the following steps when called:- Let result be ?
Call (onFinally,undefined ). - Let p be ?
PromiseResolve (C, result). - Let returnValue be a new
Abstract Closure with no parameters that captures value and performs the following steps when called:- Return value.
- Let valueThunk be
CreateBuiltinFunction (returnValue, 0,"" , « »). - Return ?
Invoke (p,"then" , « valueThunk »).
- Let result be ?
- Let thenFinally be
CreateBuiltinFunction (thenFinallyClosure, 1,"" , « »). - Let catchFinallyClosure be a new
Abstract Closure with parameters (reason) that captures onFinally and C and performs the following steps when called:- Let result be ?
Call (onFinally,undefined ). - Let p be ?
PromiseResolve (C, result). - Let throwReason be a new
Abstract Closure with no parameters that captures reason and performs the following steps when called:- Return
ThrowCompletion (reason).
- Return
- Let thrower be
CreateBuiltinFunction (throwReason, 0,"" , « »). - Return ?
Invoke (p,"then" , « thrower »).
- Let result be ?
- Let catchFinally be
CreateBuiltinFunction (catchFinallyClosure, 1,"" , « »).
- Let thenFinallyClosure be a new
- Return ?
Invoke (promise,"then" , « thenFinally, catchFinally »).
27.2.5.4 Promise.prototype.then ( onFulfilled, onRejected )
This method performs the following steps when called:
- Let promise be the
this value. - If
IsPromise (promise) isfalse , throw aTypeError exception. - Let C be ?
SpeciesConstructor (promise,%Promise% ). - Let resultCapability be ?
NewPromiseCapability (C). - Return
PerformPromiseThen (promise, onFulfilled, onRejected, resultCapability).
27.2.5.4.1 PerformPromiseThen ( promise, onFulfilled, onRejected [ , resultCapability ] )
The abstract operation PerformPromiseThen takes arguments promise (a Promise),
onFulfilled (an
Assert :IsPromise (promise) istrue .- If resultCapability is not present, then
- Set resultCapability to
undefined .
- Set resultCapability to
- If
IsCallable (onFulfilled) isfalse , then- Let onFulfilledJobCallback be
empty .
- Let onFulfilledJobCallback be
- Else,
- Let onFulfilledJobCallback be
HostMakeJobCallback (onFulfilled).
- Let onFulfilledJobCallback be
- If
IsCallable (onRejected) isfalse , then- Let onRejectedJobCallback be
empty .
- Let onRejectedJobCallback be
- Else,
- Let onRejectedJobCallback be
HostMakeJobCallback (onRejected).
- Let onRejectedJobCallback be
- Let fulfillReaction be the
PromiseReaction Record { [[Capability]]: resultCapability, [[Type]]:fulfill , [[Handler]]: onFulfilledJobCallback }. - Let rejectReaction be the
PromiseReaction Record { [[Capability]]: resultCapability, [[Type]]:reject , [[Handler]]: onRejectedJobCallback }. - If promise.[[PromiseState]]
is
pending , then- Append fulfillReaction to promise.[[PromiseFulfillReactions]].
- Append rejectReaction to promise.[[PromiseRejectReactions]].
- Else if promise.[[PromiseState]] is
fulfilled , then- Let value be promise.[[PromiseResult]].
- Let fulfillJob be
NewPromiseReactionJob (fulfillReaction, value). - Perform
HostEnqueuePromiseJob (fulfillJob.[[Job]], fulfillJob.[[Realm]]).
- Else,
Assert : The value of promise.[[PromiseState]] isrejected .- Let reason be promise.[[PromiseResult]].
- If promise.[[PromiseIsHandled]] is
false , performHostPromiseRejectionTracker (promise,"handle" ). - Let rejectJob be
NewPromiseReactionJob (rejectReaction, reason). - Perform
HostEnqueuePromiseJob (rejectJob.[[Job]], rejectJob.[[Realm]]).
- Set promise.[[PromiseIsHandled]] to
true . - If resultCapability is
undefined , then- Return
undefined .
- Return
- Else,
- Return resultCapability.[[Promise]].
27.2.5.5 Promise.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
27.2.6 Properties of Promise Instances
Promise instances are
| Internal Slot | Type | Description |
|---|---|---|
| [[PromiseState]] |
|
Governs how a promise will react to incoming calls to its then method.
|
| [[PromiseResult]] |
an |
The value with which the promise has been fulfilled or rejected, if any. Only meaningful if
[[PromiseState]] is not |
| [[PromiseFulfillReactions]] |
a |
|
| [[PromiseRejectReactions]] |
a |
|
| [[PromiseIsHandled]] | a Boolean | Indicates whether the promise has ever had a fulfillment or rejection handler; used in unhandled rejection tracking. |
27.3 GeneratorFunction Objects
GeneratorFunctions are functions that are usually created by evaluating
27.3.1 The GeneratorFunction Constructor
The GeneratorFunction
- is %GeneratorFunction%.
- is a subclass of
Function. - creates and initializes a new GeneratorFunction when called as a function rather than as a
constructor . Thus the function callGeneratorFunction (…)is equivalent to the object creation expressionnew GeneratorFunction (…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified GeneratorFunction behaviour must include asupercall to the GeneratorFunctionconstructor to create and initialize subclass instances with the internal slots necessary for built-in GeneratorFunction behaviour. All ECMAScript syntactic forms for defining generatorfunction objects create direct instances of GeneratorFunction. There is no syntactic means to create instances of GeneratorFunction subclasses.
27.3.1.1 GeneratorFunction ( ...parameterArgs, bodyArg )
The last argument (if any) specifies the body (executable code) of a generator function; any preceding arguments specify formal parameters.
This function performs the following steps when called:
- Let C be the
active function object . - If bodyArg is not present, set bodyArg to the empty String.
- Return ?
CreateDynamicFunction (C, NewTarget,generator , parameterArgs, bodyArg).
See NOTE for
27.3.2 Properties of the GeneratorFunction Constructor
The GeneratorFunction
- is a standard built-in
function object that inherits from the Functionconstructor . - has a [[Prototype]] internal slot whose value is
%Function% . - has a
"length" property whose value is1 𝔽. - has a
"name" property whose value is"GeneratorFunction" . - has the following properties:
27.3.2.1 GeneratorFunction.prototype
The initial value of GeneratorFunction.prototype is the
This property has the attributes { [[Writable]]:
27.3.3 Properties of the GeneratorFunction Prototype Object
The GeneratorFunction prototype object:
- is %GeneratorFunction.prototype% (see
Figure 6 ). - is an
ordinary object . - is not a
function object and does not have an [[ECMAScriptCode]] internal slot or any other of the internal slots listed inTable 30 orTable 88 . - has a [[Prototype]] internal slot whose value is
%Function.prototype% .
27.3.3.1 GeneratorFunction.prototype.constructor
The initial value of GeneratorFunction.prototype.constructor is
This property has the attributes { [[Writable]]:
27.3.3.2 GeneratorFunction.prototype.prototype
The initial value of GeneratorFunction.prototype.prototype is the
This property has the attributes { [[Writable]]:
27.3.3.3 GeneratorFunction.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
27.3.4 GeneratorFunction Instances
Every GeneratorFunction instance is an ECMAScript
Each GeneratorFunction instance has the following own properties:
27.3.4.1 length
The specification for the
27.3.4.2 name
The specification for the
27.3.4.3 prototype
Whenever a GeneratorFunction instance is created another
This property has the attributes { [[Writable]]:
Unlike Function instances, the object that is the value of a GeneratorFunction's
27.4 AsyncGeneratorFunction Objects
AsyncGeneratorFunctions are functions that are usually created by evaluating
27.4.1 The AsyncGeneratorFunction Constructor
The AsyncGeneratorFunction
- is %AsyncGeneratorFunction%.
- is a subclass of
Function. - creates and initializes a new AsyncGeneratorFunction when called as a function rather than as a
constructor . Thus the function callAsyncGeneratorFunction (...)is equivalent to the object creation expressionnew AsyncGeneratorFunction (...)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified AsyncGeneratorFunction behaviour must include asupercall to the AsyncGeneratorFunctionconstructor to create and initialize subclass instances with the internal slots necessary for built-in AsyncGeneratorFunction behaviour. All ECMAScript syntactic forms for defining async generatorfunction objects create direct instances of AsyncGeneratorFunction. There is no syntactic means to create instances of AsyncGeneratorFunction subclasses.
27.4.1.1 AsyncGeneratorFunction ( ...parameterArgs, bodyArg )
The last argument (if any) specifies the body (executable code) of an async generator function; any preceding arguments specify formal parameters.
This function performs the following steps when called:
- Let C be the
active function object . - If bodyArg is not present, set bodyArg to the empty String.
- Return ?
CreateDynamicFunction (C, NewTarget,async-generator , parameterArgs, bodyArg).
See NOTE for
27.4.2 Properties of the AsyncGeneratorFunction Constructor
The AsyncGeneratorFunction
- is a standard built-in
function object that inherits from the Functionconstructor . - has a [[Prototype]] internal slot whose value is
%Function% . - has a
"length" property whose value is1 𝔽. - has a
"name" property whose value is"AsyncGeneratorFunction" . - has the following properties:
27.4.2.1 AsyncGeneratorFunction.prototype
The initial value of AsyncGeneratorFunction.prototype is the
This property has the attributes { [[Writable]]:
27.4.3 Properties of the AsyncGeneratorFunction Prototype Object
The AsyncGeneratorFunction prototype object:
- is %AsyncGeneratorFunction.prototype%.
- is an
ordinary object . - is not a
function object and does not have an [[ECMAScriptCode]] internal slot or any other of the internal slots listed inTable 30 orTable 89 . - has a [[Prototype]] internal slot whose value is
%Function.prototype% .
27.4.3.1 AsyncGeneratorFunction.prototype.constructor
The initial value of AsyncGeneratorFunction.prototype.constructor is
This property has the attributes { [[Writable]]:
27.4.3.2 AsyncGeneratorFunction.prototype.prototype
The initial value of AsyncGeneratorFunction.prototype.prototype is the
This property has the attributes { [[Writable]]:
27.4.3.3 AsyncGeneratorFunction.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
27.4.4 AsyncGeneratorFunction Instances
Every AsyncGeneratorFunction instance is an ECMAScript
Each AsyncGeneratorFunction instance has the following own properties:
27.4.4.1 length
The value of the
This property has the attributes { [[Writable]]:
27.4.4.2 name
The specification for the
27.4.4.3 prototype
Whenever an AsyncGeneratorFunction instance is created, another
This property has the attributes { [[Writable]]:
Unlike function instances, the object that is the value of an AsyncGeneratorFunction's
27.5 Generator Objects
A Generator is an instance of a generator function and conforms to both the Iterator and Iterable interfaces.
Generator instances directly inherit properties from the object that is the initial value of the
27.5.1 Properties of the Generator Prototype Object
The Generator prototype object:
- is %GeneratorFunction.prototype.prototype%.
- is an
ordinary object . - is not a Generator instance and does not have a [[GeneratorState]] internal slot.
- has a [[Prototype]] internal slot whose value is
%IteratorPrototype% . - has properties that are indirectly inherited by all Generator instances.
27.5.1.1 Generator.prototype.constructor
The initial value of Generator.prototype.constructor is
This property has the attributes { [[Writable]]:
27.5.1.2 Generator.prototype.next ( value )
- Return ?
GeneratorResume (this value, value,empty ).
27.5.1.3 Generator.prototype.return ( value )
This method performs the following steps when called:
- Let g be the
this value. - Let C be
Completion Record { [[Type]]:return , [[Value]]: value, [[Target]]:empty }. - Return ?
GeneratorResumeAbrupt (g, C,empty ).
27.5.1.4 Generator.prototype.throw ( exception )
This method performs the following steps when called:
- Let g be the
this value. - Let C be
ThrowCompletion (exception). - Return ?
GeneratorResumeAbrupt (g, C,empty ).
27.5.1.5 Generator.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
27.5.2 Properties of Generator Instances
Generator instances are initially created with the internal slots described in
| Internal Slot | Type | Description |
|---|---|---|
| [[GeneratorState]] |
|
The current execution state of the generator. |
| [[GeneratorContext]] |
an |
The |
| [[GeneratorBrand]] |
a String or |
A brand used to distinguish different kinds of generators. The [[GeneratorBrand]] of generators declared by |
27.5.3 Generator Abstract Operations
27.5.3.1 GeneratorStart ( generator, generatorBody )
The abstract operation GeneratorStart takes arguments generator (a Generator) and
generatorBody (a
Assert : The value of generator.[[GeneratorState]] isundefined .- Let genContext be the
running execution context . - Set the Generator component of genContext to generator.
- Let closure be a new
Abstract Closure with no parameters that captures generatorBody and performs the following steps when called:- Let acGenContext be the
running execution context . - Let acGenerator be the Generator component of acGenContext.
- If generatorBody is a
Parse Node , then- Let result be
Completion (Evaluation of generatorBody).
- Let result be
- Else,
Assert : generatorBody is anAbstract Closure with no parameters.- Let result be generatorBody().
Assert : If we return here, the generator either threw an exception or performed either an implicit or explicit return.- Remove acGenContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - Set acGenerator.[[GeneratorState]] to
completed . - NOTE: Once a generator enters the
completed state it never leaves it and its associatedexecution context is never resumed. Any execution state associated with acGenerator can be discarded at this point. - If result is a
normal completion , then- Let resultValue be
undefined .
- Let resultValue be
- Else if result is a
return completion , then- Let resultValue be result.[[Value]].
- Else,
Assert : result is athrow completion .- Return ? result.
- Return
CreateIterResultObject (resultValue,true ).
- Let acGenContext be the
- Set the code evaluation state of genContext such
that
when evaluation is resumed for that
execution context , closure will be called with no arguments. - Set generator.[[GeneratorContext]] to genContext.
- Set generator.[[GeneratorState]] to
suspended-start . - Return
unused .
27.5.3.2 GeneratorValidate ( generator, generatorBrand )
The abstract operation GeneratorValidate takes arguments generator (an
- Perform ?
RequireInternalSlot (generator, [[GeneratorState]]). - Perform ?
RequireInternalSlot (generator, [[GeneratorBrand]]). - If generator.[[GeneratorBrand]] is not generatorBrand, throw a
TypeError exception. Assert : generator also has a [[GeneratorContext]] internal slot.- Let state be generator.[[GeneratorState]].
- If state is
executing , throw aTypeError exception. - Return state.
27.5.3.3 GeneratorResume ( generator, value, generatorBrand )
The abstract operation GeneratorResume takes arguments generator (an
- Let state be ?
GeneratorValidate (generator, generatorBrand). - If state is
completed , returnCreateIterResultObject (undefined ,true ). Assert : state is eithersuspended-start orsuspended-yield .- Let genContext be generator.[[GeneratorContext]].
- Let methodContext be the
running execution context . - Suspend methodContext.
- Set generator.[[GeneratorState]] to
executing . - Push genContext onto the
execution context stack ; genContext is now therunning execution context . - Resume the suspended evaluation of
genContext using
NormalCompletion (value) as the result of the operation that suspended it. Let result be the value returned by the resumed computation. Assert : When we return here, genContext has already been removed from theexecution context stack and methodContext is the currentlyrunning execution context .- Return ? result.
27.5.3.4 GeneratorResumeAbrupt ( generator, abruptCompletion, generatorBrand )
The abstract operation GeneratorResumeAbrupt takes arguments generator (an
- Let state be ?
GeneratorValidate (generator, generatorBrand). - If state is
suspended-start , then- Set generator.[[GeneratorState]] to
completed . - NOTE: Once a generator enters the
completed state it never leaves it and its associatedexecution context is never resumed. Any execution state associated with generator can be discarded at this point. - Set state to
completed .
- Set generator.[[GeneratorState]] to
- If state is
completed , then- If abruptCompletion is a
return completion , then- Return
CreateIterResultObject (abruptCompletion.[[Value]],true ).
- Return
- Return ? abruptCompletion.
- If abruptCompletion is a
Assert : state issuspended-yield .- Let genContext be generator.[[GeneratorContext]].
- Let methodContext be the
running execution context . - Suspend methodContext.
- Set generator.[[GeneratorState]] to
executing . - Push genContext onto the
execution context stack ; genContext is now therunning execution context . - Resume the suspended evaluation of
genContext using abruptCompletion as the result of the operation
that
suspended it. Let result be the
Completion Record returned by the resumed computation. Assert : When we return here, genContext has already been removed from theexecution context stack and methodContext is the currentlyrunning execution context .- Return ? result.
27.5.3.5 GetGeneratorKind ( )
The abstract operation GetGeneratorKind takes no arguments and returns
- Let genContext be the
running execution context . - If genContext does not have a Generator component,
return
non-generator . - Let generator be the Generator component of genContext.
- If generator has an [[AsyncGeneratorState]] internal slot, return
async . - Else, return
sync .
27.5.3.6 GeneratorYield ( iterNextObj )
The abstract operation GeneratorYield takes argument iterNextObj (an Object that conforms
to
the IteratorResult interface) and returns either a
- Let genContext be the
running execution context . Assert : genContext is theexecution context of a generator.- Let generator be the value of the Generator component of genContext.
Assert :GetGeneratorKind () issync .- Set generator.[[GeneratorState]] to
suspended-yield . - Remove genContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - Let callerContext be the
running execution context . - Resume callerContext passing
NormalCompletion (iterNextObj). If genContext is ever resumed again, let resumptionValue be theCompletion Record with which it is resumed. Assert : If control reaches here, then genContext is therunning execution context again.- Return resumptionValue.
27.5.3.7 Yield ( value )
The abstract operation Yield takes argument value (an
- Let generatorKind be
GetGeneratorKind (). - If generatorKind is
async , return ?AsyncGeneratorYield (?Await (value)). - Otherwise, return ?
GeneratorYield (CreateIterResultObject (value,false )).
27.5.3.8 CreateIteratorFromClosure ( closure, generatorBrand, generatorPrototype )
The abstract operation CreateIteratorFromClosure takes arguments closure (an
- NOTE: closure can contain uses of the
Yield operation to yield an IteratorResult object. - Let internalSlotsList be « [[GeneratorState]], [[GeneratorContext]], [[GeneratorBrand]] ».
- Let generator be
OrdinaryObjectCreate (generatorPrototype, internalSlotsList). - Set generator.[[GeneratorBrand]] to generatorBrand.
- Set generator.[[GeneratorState]] to
undefined . - Let callerContext be the
running execution context . - Let calleeContext be a new
execution context . - Set the Function of calleeContext to
null . - Set the
Realm of calleeContext tothe current Realm Record . - Set the ScriptOrModule of calleeContext to callerContext's ScriptOrModule.
- If callerContext is not already suspended, suspend callerContext.
- Push calleeContext onto the
execution context stack ; calleeContext is now therunning execution context . - Perform
GeneratorStart (generator, closure). - Remove calleeContext from the
execution context stack and restore callerContext as therunning execution context . - Return generator.
27.6 AsyncGenerator Objects
An AsyncGenerator is an instance of an async generator function and conforms to both the AsyncIterator and AsyncIterable interfaces.
AsyncGenerator instances directly inherit properties from the object that is the initial value of the
27.6.1 Properties of the AsyncGenerator Prototype Object
The AsyncGenerator prototype object:
- is %AsyncGeneratorFunction.prototype.prototype%.
- is an
ordinary object . - is not an AsyncGenerator instance and does not have an [[AsyncGeneratorState]] internal slot.
- has a [[Prototype]] internal slot whose value is
%AsyncIteratorPrototype% . - has properties that are indirectly inherited by all AsyncGenerator instances.
27.6.1.1 AsyncGenerator.prototype.constructor
The initial value of AsyncGenerator.prototype.constructor is
This property has the attributes { [[Writable]]:
27.6.1.2 AsyncGenerator.prototype.next ( value )
- Let generator be the
this value. - Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let result be
Completion (AsyncGeneratorValidate (generator,empty )). IfAbruptRejectPromise (result, promiseCapability).- Let state be generator.[[AsyncGeneratorState]].
- If state is
completed , then- Let iteratorResult be
CreateIterResultObject (undefined ,true ). - Perform !
Call (promiseCapability.[[Resolve]],undefined , « iteratorResult »). - Return promiseCapability.[[Promise]].
- Let iteratorResult be
- Let completion be
NormalCompletion (value). - Perform
AsyncGeneratorEnqueue (generator, completion, promiseCapability). - If state is either
suspended-start orsuspended-yield , then- Perform
AsyncGeneratorResume (generator, completion).
- Perform
- Else,
Assert : state is eitherexecuting orawaiting-return .
- Return promiseCapability.[[Promise]].
27.6.1.3 AsyncGenerator.prototype.return ( value )
- Let generator be the
this value. - Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let result be
Completion (AsyncGeneratorValidate (generator,empty )). IfAbruptRejectPromise (result, promiseCapability).- Let completion be
Completion Record { [[Type]]:return , [[Value]]: value, [[Target]]:empty }. - Perform
AsyncGeneratorEnqueue (generator, completion, promiseCapability). - Let state be generator.[[AsyncGeneratorState]].
- If state is either
suspended-start orcompleted , then- Set generator.[[AsyncGeneratorState]] to
awaiting-return . - Perform !
AsyncGeneratorAwaitReturn (generator).
- Set generator.[[AsyncGeneratorState]] to
- Else if state is
suspended-yield , then- Perform
AsyncGeneratorResume (generator, completion).
- Perform
- Else,
Assert : state is eitherexecuting orawaiting-return .
- Return promiseCapability.[[Promise]].
27.6.1.4 AsyncGenerator.prototype.throw ( exception )
- Let generator be the
this value. - Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let result be
Completion (AsyncGeneratorValidate (generator,empty )). IfAbruptRejectPromise (result, promiseCapability).- Let state be generator.[[AsyncGeneratorState]].
- If state is
suspended-start , then- Set generator.[[AsyncGeneratorState]] to
completed . - Set state to
completed .
- Set generator.[[AsyncGeneratorState]] to
- If state is
completed , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « exception »). - Return promiseCapability.[[Promise]].
- Perform !
- Let completion be
ThrowCompletion (exception). - Perform
AsyncGeneratorEnqueue (generator, completion, promiseCapability). - If state is
suspended-yield , then- Perform
AsyncGeneratorResume (generator, completion).
- Perform
- Else,
Assert : state is eitherexecuting orawaiting-return .
- Return promiseCapability.[[Promise]].
27.6.1.5 AsyncGenerator.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
27.6.2 Properties of AsyncGenerator Instances
AsyncGenerator instances are initially created with the internal slots described below:
| Internal Slot | Type | Description |
|---|---|---|
| [[AsyncGeneratorState]] | The current execution state of the async generator. | |
| [[AsyncGeneratorContext]] | an |
The |
| [[AsyncGeneratorQueue]] | a |
|
| [[GeneratorBrand]] | a String or |
A brand used to distinguish different kinds of async generators. The [[GeneratorBrand]] of async generators declared by |
27.6.3 AsyncGenerator Abstract Operations
27.6.3.1 AsyncGeneratorRequest Records
An AsyncGeneratorRequest is a
They have the following fields:
| Field Name | Value | Meaning |
|---|---|---|
| [[Completion]] | a |
The |
| [[Capability]] | a |
The promise capabilities associated with this request. |
27.6.3.2 AsyncGeneratorStart ( generator, generatorBody )
The abstract operation AsyncGeneratorStart takes arguments generator (an AsyncGenerator)
and
generatorBody (a
Assert : generator.[[AsyncGeneratorState]] isundefined .- Let genContext be the
running execution context . - Set the Generator component of genContext to generator.
- Let closure be a new
Abstract Closure with no parameters that captures generatorBody and performs the following steps when called:- Let acGenContext be the
running execution context . - Let acGenerator be the Generator component of acGenContext.
- If generatorBody is a
Parse Node , then- Let result be
Completion (Evaluation of generatorBody).
- Let result be
- Else,
Assert : generatorBody is anAbstract Closure with no parameters.- Let result be
Completion (generatorBody()).
Assert : If we return here, the async generator either threw an exception or performed either an implicit or explicit return.- Remove acGenContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - Set acGenerator.[[AsyncGeneratorState]] to
completed . - If result is a
normal completion , set result toNormalCompletion (undefined ). - If result is a
return completion , set result toNormalCompletion (result.[[Value]]). - Perform
AsyncGeneratorCompleteStep (acGenerator, result,true ). - Perform
AsyncGeneratorDrainQueue (acGenerator). - Return
undefined .
- Let acGenContext be the
- Set the code evaluation state of genContext such
that
when evaluation is resumed for that
execution context , closure will be called with no arguments. - Set generator.[[AsyncGeneratorContext]] to genContext.
- Set generator.[[AsyncGeneratorState]] to
suspended-start . - Set generator.[[AsyncGeneratorQueue]] to a new empty
List . - Return
unused .
27.6.3.3 AsyncGeneratorValidate ( generator, generatorBrand )
The abstract operation AsyncGeneratorValidate takes arguments generator (an
- Perform ?
RequireInternalSlot (generator, [[AsyncGeneratorContext]]). - Perform ?
RequireInternalSlot (generator, [[AsyncGeneratorState]]). - Perform ?
RequireInternalSlot (generator, [[AsyncGeneratorQueue]]). - If generator.[[GeneratorBrand]] is not generatorBrand, throw a
TypeError exception. - Return
unused .
27.6.3.4 AsyncGeneratorEnqueue ( generator, completion, promiseCapability )
The abstract operation AsyncGeneratorEnqueue takes arguments generator (an
AsyncGenerator),
completion (a
- Let request be
AsyncGeneratorRequest { [[Completion]]: completion, [[Capability]]: promiseCapability }. - Append request to generator.[[AsyncGeneratorQueue]].
- Return
unused .
27.6.3.5 AsyncGeneratorCompleteStep ( generator, completion, done [ , realm ] )
The abstract operation AsyncGeneratorCompleteStep takes arguments generator (an
AsyncGenerator), completion (a
Assert : generator.[[AsyncGeneratorQueue]] is not empty.- Let next be the first element of generator.[[AsyncGeneratorQueue]].
- Remove the first element from generator.[[AsyncGeneratorQueue]].
- Let promiseCapability be next.[[Capability]].
- Let value be completion.[[Value]].
- If completion is a
throw completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « value »).
- Perform !
- Else,
Assert : completion is anormal completion .- If realm is present, then
- Let oldRealm be the
running execution context 'sRealm . - Set the
running execution context 'sRealm to realm. - Let iteratorResult be
CreateIterResultObject (value, done). - Set the
running execution context 'sRealm to oldRealm.
- Let oldRealm be the
- Else,
- Let iteratorResult be
CreateIterResultObject (value, done).
- Let iteratorResult be
- Perform !
Call (promiseCapability.[[Resolve]],undefined , « iteratorResult »).
- Return
unused .
27.6.3.6 AsyncGeneratorResume ( generator, completion )
The abstract operation AsyncGeneratorResume takes arguments generator (an AsyncGenerator)
and
completion (a
Assert : generator.[[AsyncGeneratorState]] is eithersuspended-start orsuspended-yield .- Let genContext be generator.[[AsyncGeneratorContext]].
- Let callerContext be the
running execution context . - Suspend callerContext.
- Set generator.[[AsyncGeneratorState]] to
executing . - Push genContext onto the
execution context stack ; genContext is now therunning execution context . - Resume the suspended evaluation of
genContext using completion as the result of the operation that
suspended it. Let result be the
Completion Record returned by the resumed computation. Assert : result is never anabrupt completion .Assert : When we return here, genContext has already been removed from theexecution context stack and callerContext is the currentlyrunning execution context .- Return
unused .
27.6.3.7 AsyncGeneratorUnwrapYieldResumption ( resumptionValue )
The abstract operation AsyncGeneratorUnwrapYieldResumption takes argument resumptionValue
(a
- If resumptionValue is not a
return completion , return ? resumptionValue. - Let awaited be
Completion (Await (resumptionValue.[[Value]])). - If awaited is a
throw completion , return ? awaited. Assert : awaited is anormal completion .- Return
Completion Record { [[Type]]:return , [[Value]]: awaited.[[Value]], [[Target]]:empty }.
27.6.3.8 AsyncGeneratorYield ( value )
The abstract operation AsyncGeneratorYield takes argument value (an
- Let genContext be the
running execution context . Assert : genContext is theexecution context of a generator.- Let generator be the value of the Generator component of genContext.
Assert :GetGeneratorKind () isasync .- Let completion be
NormalCompletion (value). Assert : Theexecution context stack has at least two elements.- Let previousContext be the second to top element
of
the
execution context stack . - Let previousRealm be previousContext's
Realm . - Perform
AsyncGeneratorCompleteStep (generator, completion,false , previousRealm). - Let queue be generator.[[AsyncGeneratorQueue]].
- If queue is not empty, then
- NOTE: Execution continues without suspending the generator.
- Let toYield be the first element of queue.
- Let resumptionValue be
Completion (toYield.[[Completion]]). - Return ?
AsyncGeneratorUnwrapYieldResumption (resumptionValue).
- Else,
- Set generator.[[AsyncGeneratorState]] to
suspended-yield . - Remove genContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - Let callerContext be the
running execution context . - Resume callerContext passing
undefined . If genContext is ever resumed again, let resumptionValue be theCompletion Record with which it is resumed. Assert : If control reaches here, then genContext is therunning execution context again.- Return ?
AsyncGeneratorUnwrapYieldResumption (resumptionValue).
- Set generator.[[AsyncGeneratorState]] to
27.6.3.9 AsyncGeneratorAwaitReturn ( generator )
The abstract operation AsyncGeneratorAwaitReturn takes argument generator (an
AsyncGenerator)
and returns either a
- Let queue be generator.[[AsyncGeneratorQueue]].
Assert : queue is not empty.- Let next be the first element of queue.
- Let completion be
Completion (next.[[Completion]]). Assert : completion is areturn completion .- Let promise be ?
PromiseResolve (%Promise% , completion.[[Value]]). - Let fulfilledClosure be a new
Abstract Closure with parameters (value) that captures generator and performs the following steps when called:- Set generator.[[AsyncGeneratorState]] to
completed . - Let result be
NormalCompletion (value). - Perform
AsyncGeneratorCompleteStep (generator, result,true ). - Perform
AsyncGeneratorDrainQueue (generator). - Return
undefined .
- Set generator.[[AsyncGeneratorState]] to
- Let onFulfilled be
CreateBuiltinFunction (fulfilledClosure, 1,"" , « »). - Let rejectedClosure be a new
Abstract Closure with parameters (reason) that captures generator and performs the following steps when called:- Set generator.[[AsyncGeneratorState]] to
completed . - Let result be
ThrowCompletion (reason). - Perform
AsyncGeneratorCompleteStep (generator, result,true ). - Perform
AsyncGeneratorDrainQueue (generator). - Return
undefined .
- Set generator.[[AsyncGeneratorState]] to
- Let onRejected be
CreateBuiltinFunction (rejectedClosure, 1,"" , « »). - Perform
PerformPromiseThen (promise, onFulfilled, onRejected). - Return
unused .
27.6.3.10 AsyncGeneratorDrainQueue ( generator )
The abstract operation AsyncGeneratorDrainQueue takes argument generator (an
AsyncGenerator)
and returns
Assert : generator.[[AsyncGeneratorState]] iscompleted .- Let queue be generator.[[AsyncGeneratorQueue]].
- If queue is empty, return
unused . - Let done be
false . - Repeat, while done is
false ,- Let next be the first element of queue.
- Let completion be
Completion (next.[[Completion]]). - If completion is a
return completion , then- Set generator.[[AsyncGeneratorState]] to
awaiting-return . - Perform !
AsyncGeneratorAwaitReturn (generator). - Set done to
true .
- Set generator.[[AsyncGeneratorState]] to
- Else,
- If completion is a
normal completion , then- Set completion to
NormalCompletion (undefined ).
- Set completion to
- Perform
AsyncGeneratorCompleteStep (generator, completion,true ). - If queue is empty, set done
to
true .
- If completion is a
- Return
unused .
27.6.3.11 CreateAsyncIteratorFromClosure ( closure, generatorBrand, generatorPrototype )
The abstract operation CreateAsyncIteratorFromClosure takes arguments closure (an
- NOTE: closure can contain uses of the
Await operation and uses of theYield operation to yield an IteratorResult object. - Let internalSlotsList be « [[AsyncGeneratorState]], [[AsyncGeneratorContext]], [[AsyncGeneratorQueue]], [[GeneratorBrand]] ».
- Let generator be
OrdinaryObjectCreate (generatorPrototype, internalSlotsList). - Set generator.[[GeneratorBrand]] to generatorBrand.
- Set generator.[[AsyncGeneratorState]] to
undefined . - Let callerContext be the
running execution context . - Let calleeContext be a new
execution context . - Set the Function of calleeContext to
null . - Set the
Realm of calleeContext tothe current Realm Record . - Set the ScriptOrModule of calleeContext to callerContext's ScriptOrModule.
- If callerContext is not already suspended, suspend callerContext.
- Push calleeContext onto the
execution context stack ; calleeContext is now therunning execution context . - Perform
AsyncGeneratorStart (generator, closure). - Remove calleeContext from the
execution context stack and restore callerContext as therunning execution context . - Return generator.
27.7 AsyncFunction Objects
AsyncFunctions are functions that are usually created by evaluating
27.7.1 The AsyncFunction Constructor
The AsyncFunction
- is %AsyncFunction%.
- is a subclass of
Function. - creates and initializes a new AsyncFunction when called as a function rather than as a
constructor . Thus the function callAsyncFunction(…)is equivalent to the object creation expressionnew AsyncFunction(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified AsyncFunction behaviour must include asupercall to the AsyncFunctionconstructor to create and initialize a subclass instance with the internal slots necessary for built-in async function behaviour. All ECMAScript syntactic forms for defining asyncfunction objects create direct instances of AsyncFunction. There is no syntactic means to create instances of AsyncFunction subclasses.
27.7.1.1 AsyncFunction ( ...parameterArgs, bodyArg )
The last argument (if any) specifies the body (executable code) of an async function. Any preceding arguments specify formal parameters.
This function performs the following steps when called:
- Let C be the
active function object . - If bodyArg is not present, set bodyArg to the empty String.
- Return ?
CreateDynamicFunction (C, NewTarget,async , parameterArgs, bodyArg).
27.7.2 Properties of the AsyncFunction Constructor
The AsyncFunction
- is a standard built-in
function object that inherits from the Functionconstructor . - has a [[Prototype]] internal slot whose value is
%Function% . - has a
"length" property whose value is1 𝔽. - has a
"name" property whose value is"AsyncFunction" . - has the following properties:
27.7.2.1 AsyncFunction.prototype
The initial value of AsyncFunction.prototype is the
This property has the attributes { [[Writable]]:
27.7.3 Properties of the AsyncFunction Prototype Object
The AsyncFunction prototype object:
- is %AsyncFunction.prototype%.
- is an
ordinary object . - is not a
function object and does not have an [[ECMAScriptCode]] internal slot or any other of the internal slots listed inTable 30 . - has a [[Prototype]] internal slot whose value is
%Function.prototype% .
27.7.3.1 AsyncFunction.prototype.constructor
The initial value of AsyncFunction.prototype.constructor is
This property has the attributes { [[Writable]]:
27.7.3.2 AsyncFunction.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
27.7.4 AsyncFunction Instances
Every AsyncFunction instance is an ECMAScript
Each AsyncFunction instance has the following own properties:
27.7.4.1 length
The specification for the
27.7.4.2 name
The specification for the
27.7.5 Async Functions Abstract Operations
27.7.5.1 AsyncFunctionStart ( promiseCapability, asyncFunctionBody )
The abstract operation AsyncFunctionStart takes arguments promiseCapability (a
- Let runningContext be the
running execution context . - Let asyncContext be a copy of runningContext.
- NOTE: Copying the execution state is required for
AsyncBlockStart to resume its execution. It is ill-defined to resume a currently executing context. - Perform
AsyncBlockStart (promiseCapability, asyncFunctionBody, asyncContext). - Return
unused .
27.7.5.2 AsyncBlockStart ( promiseCapability, asyncBody, asyncContext )
The abstract operation AsyncBlockStart takes arguments promiseCapability (a
Assert : promiseCapability is aPromiseCapability Record .- Let runningContext be the
running execution context . - Let closure be a new
Abstract Closure with no parameters that captures promiseCapability and asyncBody and performs the following steps when called:- Let acAsyncContext be the
running execution context . - Let result be
Completion (Evaluation of asyncBody). Assert : If we return here, the async function either threw an exception or performed an implicit or explicit return; all awaiting is done.- Remove acAsyncContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - If result is a
normal completion , then- Perform !
Call (promiseCapability.[[Resolve]],undefined , «undefined »).
- Perform !
- Else if result is a
return completion , then- Perform !
Call (promiseCapability.[[Resolve]],undefined , « result.[[Value]] »).
- Perform !
- Else,
Assert : result is athrow completion .- Perform !
Call (promiseCapability.[[Reject]],undefined , « result.[[Value]] »).
- Return
unused .
- Let acAsyncContext be the
- Set the code evaluation state of asyncContext such
that when evaluation is resumed for that
execution context , closure will be called with no arguments. - Push asyncContext onto the
execution context stack ; asyncContext is now therunning execution context . - Resume the suspended evaluation of asyncContext. Let result be the value returned by the resumed computation.
Assert : When we return here, asyncContext has already been removed from theexecution context stack and runningContext is the currentlyrunning execution context .Assert : result is anormal completion with a value ofunused . The possible sources of this value areAwait or, if the async function doesn't await anything, step3.h above.- Return
unused .
27.7.5.3 Await ( value )
The abstract operation Await takes argument value (an
- Let asyncContext be the
running execution context . - Let promise be ?
PromiseResolve (%Promise% , value). - Let fulfilledClosure be a new
Abstract Closure with parameters (v) that captures asyncContext and performs the following steps when called:- Let prevContext be the
running execution context . - Suspend prevContext.
- Push asyncContext onto the
execution context stack ; asyncContext is now therunning execution context . - Resume the suspended evaluation
of
asyncContext using
NormalCompletion (v) as the result of the operation that suspended it. Assert : When we reach this step, asyncContext has already been removed from theexecution context stack and prevContext is the currentlyrunning execution context .- Return
undefined .
- Let prevContext be the
- Let onFulfilled be
CreateBuiltinFunction (fulfilledClosure, 1,"" , « »). - Let rejectedClosure be a new
Abstract Closure with parameters (reason) that captures asyncContext and performs the following steps when called:- Let prevContext be the
running execution context . - Suspend prevContext.
- Push asyncContext onto the
execution context stack ; asyncContext is now therunning execution context . - Resume the suspended evaluation
of
asyncContext using
ThrowCompletion (reason) as the result of the operation that suspended it. Assert : When we reach this step, asyncContext has already been removed from theexecution context stack and prevContext is the currentlyrunning execution context .- Return
undefined .
- Let prevContext be the
- Let onRejected be
CreateBuiltinFunction (rejectedClosure, 1,"" , « »). - Perform
PerformPromiseThen (promise, onFulfilled, onRejected). - Remove asyncContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - Let callerContext be the
running execution context . - Resume callerContext passing
empty . If asyncContext is ever resumed again, let completion be theCompletion Record with which it is resumed. Assert : If control reaches here, then asyncContext is therunning execution context again.- Return completion.
28 Reflection
28.1 The Reflect Object
The Reflect object:
- is %Reflect%.
- is the initial value of the
"Reflect" property of theglobal object . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is not a
function object . - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a [[Call]] internal method; it cannot be invoked as a function.
28.1.1 Reflect.apply ( target, thisArgument, argumentsList )
This function performs the following steps when called:
- If
IsCallable (target) isfalse , throw aTypeError exception. - Let args be ?
CreateListFromArrayLike (argumentsList). - Perform
PrepareForTailCall (). - Return ?
Call (target, thisArgument, args).
28.1.2 Reflect.construct ( target, argumentsList [ , newTarget ] )
This function performs the following steps when called:
- If
IsConstructor (target) isfalse , throw aTypeError exception. - If newTarget is not present, set newTarget to target.
- Else if
IsConstructor (newTarget) isfalse , throw aTypeError exception. - Let args be ?
CreateListFromArrayLike (argumentsList). - Return ?
Construct (target, args, newTarget).
28.1.3 Reflect.defineProperty ( target, propertyKey, attributes )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (propertyKey). - Let desc be ?
ToPropertyDescriptor (attributes). - Return ? target.[[DefineOwnProperty]](key, desc).
28.1.4 Reflect.deleteProperty ( target, propertyKey )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (propertyKey). - Return ? target.[[Delete]](key).
28.1.5 Reflect.get ( target, propertyKey [ , receiver ] )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (propertyKey). - If receiver is not present, then
- Set receiver to target.
- Return ? target.[[Get]](key, receiver).
28.1.6 Reflect.getOwnPropertyDescriptor ( target, propertyKey )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (propertyKey). - Let desc be ? target.[[GetOwnProperty]](key).
- Return
FromPropertyDescriptor (desc).
28.1.7 Reflect.getPrototypeOf ( target )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Return ? target.[[GetPrototypeOf]]().
28.1.8 Reflect.has ( target, propertyKey )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (propertyKey). - Return ? target.[[HasProperty]](key).
28.1.9 Reflect.isExtensible ( target )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Return ? target.[[IsExtensible]]().
28.1.10 Reflect.ownKeys ( target )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let keys be ? target.[[OwnPropertyKeys]]().
- Return
CreateArrayFromList (keys).
28.1.11 Reflect.preventExtensions ( target )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Return ? target.[[PreventExtensions]]().
28.1.12 Reflect.set ( target, propertyKey, V [ , receiver ] )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (propertyKey). - If receiver is not present, then
- Set receiver to target.
- Return ? target.[[Set]](key, V, receiver).
28.1.13 Reflect.setPrototypeOf ( target, proto )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - If proto
is not an Object and proto is notnull , throw aTypeError exception. - Return ? target.[[SetPrototypeOf]](proto).
28.1.14 Reflect [ @@toStringTag ]
The initial value of the
This property has the attributes { [[Writable]]:
28.2 Proxy Objects
28.2.1 The Proxy Constructor
The Proxy
- is %Proxy%.
- is the initial value of the
"Proxy" property of theglobal object . - creates and initializes a new Proxy object when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
28.2.1.1 Proxy ( target, handler )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Return ?
ProxyCreate (target, handler).
28.2.2 Properties of the Proxy Constructor
The Proxy
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - does not have a
"prototype" property because Proxy objects do not have a [[Prototype]] internal slot that requires initialization. - has the following properties:
28.2.2.1 Proxy.revocable ( target, handler )
This function creates a revocable Proxy object.
It performs the following steps when called:
- Let proxy be ?
ProxyCreate (target, handler). - Let revokerClosure be a new
Abstract Closure with no parameters that captures nothing and performs the following steps when called:- Let F be the
active function object . - Let p be F.[[RevocableProxy]].
- If p is
null , returnundefined . - Set F.[[RevocableProxy]]
to
null . Assert : p is aProxy exotic object .- Set p.[[ProxyTarget]]
to
null . - Set p.[[ProxyHandler]]
to
null . - Return
undefined .
- Let F be the
- Let revoker be
CreateBuiltinFunction (revokerClosure, 0,"" , « [[RevocableProxy]] »). - Set revoker.[[RevocableProxy]] to proxy.
- Let result be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (result,"proxy" , proxy). - Perform !
CreateDataPropertyOrThrow (result,"revoke" , revoker). - Return result.
28.3 Module Namespace Objects
A Module Namespace Object is a
In addition to the properties specified in
28.3.1 @@toStringTag
The initial value of the
This property has the attributes { [[Writable]]:
29 Memory Model
The memory consistency model, or memory model, specifies the possible orderings of
The memory model is defined as relational constraints on events introduced by
This section provides an axiomatic model on events introduced by the
29.1 Memory Model Fundamentals
Shared memory accesses (reads and writes) are divided into two groups, atomic accesses and data accesses,
defined below. Atomic accesses are sequentially consistent, i.e., there is a strict total ordering of
events
agreed upon by all
No orderings weaker than sequentially consistent and stronger than unordered, such as release-acquire, are supported.
A Shared Data Block event is either a ReadSharedMemory, WriteSharedMemory, or ReadModifyWriteSharedMemory
| Field Name | Value | Meaning |
|---|---|---|
| [[Order]] | The weakest ordering guaranteed by the |
|
| [[NoTear]] | a Boolean | Whether this event is allowed to read from multiple write events with equal range as this event. |
| [[Block]] | a |
The block the event operates on. |
| [[ByteIndex]] | a non-negative |
The byte address of the read in [[Block]]. |
| [[ElementSize]] | a non-negative |
The size of the read. |
| Field Name | Value | Meaning |
|---|---|---|
| [[Order]] | The weakest ordering guaranteed by the |
|
| [[NoTear]] | a Boolean | Whether this event is allowed to be read from multiple read events with equal range as this event. |
| [[Block]] | a |
The block the event operates on. |
| [[ByteIndex]] | a non-negative |
The byte address of the write in [[Block]]. |
| [[ElementSize]] | a non-negative |
The size of the write. |
| [[Payload]] | a |
The |
| Field Name | Value | Meaning |
|---|---|---|
| [[Order]] | Read-modify-write events are always sequentially consistent. | |
| [[NoTear]] | Read-modify-write events cannot tear. | |
| [[Block]] | a |
The block the event operates on. |
| [[ByteIndex]] | a non-negative |
The byte address of the read-modify-write in [[Block]]. |
| [[ElementSize]] | a non-negative |
The size of the read-modify-write. |
| [[Payload]] | a |
The |
| [[ModifyOp]] | a |
An abstract closure that returns a modified |
These events are introduced by
Some operations may also introduce Synchronize events. A Synchronize event has no fields, and exists purely to directly constrain the permitted orderings of other events.
In addition to
Let the range of a ReadSharedMemory, WriteSharedMemory, or ReadModifyWriteSharedMemory event be the Set
of
contiguous
Examples of postMessage in a browser), starting and stopping
Events are ordered within
29.2 Agent Events Records
An Agent Events Record is a
| Field Name | Value | Meaning |
|---|---|---|
| [[AgentSignifier]] | an |
The |
| [[EventList]] | a |
Events are appended to the list during evaluation. |
| [[AgentSynchronizesWith]] | a |
29.3 Chosen Value Records
A Chosen Value Record is a
| Field Name | Value | Meaning |
|---|---|---|
| [[Event]] | a |
The |
| [[ChosenValue]] | a |
The bytes that were nondeterministically chosen during evaluation. |
29.4 Candidate Executions
A candidate execution of the evaluation of an
| Field Name | Value | Meaning |
|---|---|---|
| [[EventsRecords]] | a |
Maps an |
| [[ChosenValues]] | a |
Maps |
| [[AgentOrder]] | an |
Defined below. |
| [[ReadsBytesFrom]] | a |
Defined below. |
| [[ReadsFrom]] | a |
Defined below. |
| [[HostSynchronizesWith]] | a |
Defined below. |
| [[SynchronizesWith]] | a |
Defined below. |
| [[HappensBefore]] | a |
Defined below. |
An empty candidate execution is a
candidate
execution
29.5 Abstract Operations for the Memory Model
29.5.1 EventSet ( execution )
The abstract operation EventSet takes argument execution (a
- Let events be an empty Set.
- For each
Agent Events Record aer of execution.[[EventsRecords]], do- For each event E of aer.[[EventList]], do
- Add E to events.
- For each event E of aer.[[EventList]], do
- Return events.
29.5.2 SharedDataBlockEventSet ( execution )
The abstract operation SharedDataBlockEventSet takes argument execution (a
- Let events be an empty Set.
- For each event E of
EventSet (execution), do- If E is a
ReadSharedMemory ,WriteSharedMemory , orReadModifyWriteSharedMemory event, add E to events.
- If E is a
- Return events.
29.5.3 HostEventSet ( execution )
The abstract operation HostEventSet takes argument execution (a
- Let events be an empty Set.
- For each event E of
EventSet (execution), do- If E is not in
SharedDataBlockEventSet (execution), add E to events.
- If E is not in
- Return events.
29.5.4 ComposeWriteEventBytes ( execution, byteIndex, Ws )
The abstract operation ComposeWriteEventBytes takes arguments execution (a
- Let byteLocation be byteIndex.
- Let bytesRead be a new empty
List . - For each element W of Ws, do
Assert : W has byteLocation in its range.- Let payloadIndex be byteLocation - W.[[ByteIndex]].
- If W is a
WriteSharedMemory event, then- Let byte be W.[[Payload]][payloadIndex].
- Else,
Assert : W is aReadModifyWriteSharedMemory event.- Let bytes be
ValueOfReadEvent (execution, W). - Let bytesModified be W.[[ModifyOp]](bytes, W.[[Payload]]).
- Let byte be bytesModified[payloadIndex].
- Append byte to bytesRead.
- Set byteLocation to byteLocation + 1.
- Return bytesRead.
The read-modify-write modification [[ModifyOp]] is given by the function
properties on the Atomics object that introduce
This abstract operation composes a
29.5.5 ValueOfReadEvent ( execution, R )
The abstract operation ValueOfReadEvent takes arguments execution (a
- Let Ws be execution.[[ReadsBytesFrom]](R).
Assert : Ws is aList ofWriteSharedMemory orReadModifyWriteSharedMemory events with length equal to R.[[ElementSize]].- Return
ComposeWriteEventBytes (execution, R.[[ByteIndex]], Ws).
29.6 Relations of Candidate Executions
29.6.1 agent-order
For a
- For each pair (E, D) in
EventSet (execution), execution.[[AgentOrder]] contains (E, D) if there is someAgent Events Record aer in execution.[[EventsRecords]] such that E and D are in aer.[[EventList]] and E is before D inList order of aer.[[EventList]].
Each
29.6.2 reads-bytes-from
For a
-
For each
ReadSharedMemory orReadModifyWriteSharedMemory event R inSharedDataBlockEventSet (execution), execution.[[ReadsBytesFrom]](R) is aList of length R.[[ElementSize]] whose elements areWriteSharedMemory orReadModifyWriteSharedMemory events Ws such that all of the following are true.- Each event W with index i in Ws has R.[[ByteIndex]] + i in its range.
- R is not in Ws.
29.6.3 reads-from
For a
- For each pair (R, W) in
SharedDataBlockEventSet (execution), execution.[[ReadsFrom]] contains (R, W) if execution.[[ReadsBytesFrom]](R) contains W.
29.6.4 host-synchronizes-with
For a
- If execution.[[HostSynchronizesWith]] contains (E,
D), E and D are in
HostEventSet (execution). - There is no cycle in the union of execution.[[HostSynchronizesWith]] and execution.[[AgentOrder]].
For two
The host-synchronizes-with relation allows the postMessage between HTML workers.
29.6.5 synchronizes-with
For a
-
For each pair (R, W) in execution.[[ReadsFrom]],
execution.[[SynchronizesWith]] contains (W,
R)
if R.[[Order]] is
seq-cst , W.[[Order]] isseq-cst , and R and W have equal ranges. -
For each element eventsRecord of execution.[[EventsRecords]], the following is true.
- For each pair (S, Sw) in eventsRecord.[[AgentSynchronizesWith]], execution.[[SynchronizesWith]] contains (S, Sw).
- For each pair (E, D) in execution.[[HostSynchronizesWith]], execution.[[SynchronizesWith]] contains (E, D).
Owing to convention, write events synchronizes-with read events, instead of read events synchronizes-with write events.
Not all
For
29.6.6 happens-before
For a
- For each pair (E, D) in execution.[[AgentOrder]], execution.[[HappensBefore]] contains (E, D).
- For each pair (E, D) in execution.[[SynchronizesWith]], execution.[[HappensBefore]] contains (E, D).
- For each pair (E, D) in
SharedDataBlockEventSet (execution), execution.[[HappensBefore]] contains (E, D) if E.[[Order]] isinit and E and D have overlapping ranges. - For each pair (E, D) in
EventSet (execution), execution.[[HappensBefore]] contains (E, D) if there is an event F such that the pairs (E, F) and (F, D) are in execution.[[HappensBefore]].
Because happens-before is a superset of
29.7 Properties of Valid Executions
29.7.1 Valid Chosen Reads
A
- For each
ReadSharedMemory orReadModifyWriteSharedMemory event R ofSharedDataBlockEventSet (execution), do- Let chosenValueRecord be the element of execution.[[ChosenValues]] whose [[Event]] field is R.
- Let chosenValue be chosenValueRecord.[[ChosenValue]].
- Let readValue be
ValueOfReadEvent (execution, R). - Let chosenLen be the number of elements in chosenValue.
- Let readLen be the number of elements in readValue.
- If chosenLen ≠ readLen, then
- Return
false .
- Return
- If chosenValue[i] ≠
readValue[i] for some
integer i in theinterval from 0 (inclusive) to chosenLen (exclusive), then- Return
false .
- Return
- Return
true .
29.7.2 Coherent Reads
A
- For each
ReadSharedMemory orReadModifyWriteSharedMemory event R ofSharedDataBlockEventSet (execution), do- Let Ws be execution.[[ReadsBytesFrom]](R).
- Let byteLocation be R.[[ByteIndex]].
- For each element W of Ws, do
- If execution.[[HappensBefore]] contains (R, W), then
- Return
false .
- Return
- If there exists a
WriteSharedMemory orReadModifyWriteSharedMemory event V that has byteLocation in its range such that the pairs (W, V) and (V, R) are in execution.[[HappensBefore]], then- Return
false .
- Return
- Set byteLocation to byteLocation + 1.
- If execution.[[HappensBefore]] contains (R, W), then
- Return
true .
29.7.3 Tear Free Reads
A
- For each
ReadSharedMemory orReadModifyWriteSharedMemory event R ofSharedDataBlockEventSet (execution), do- If R.[[NoTear]] is
true , thenAssert : The remainder of dividing R.[[ByteIndex]] by R.[[ElementSize]] is 0.- For each event W such that
execution.[[ReadsFrom]] contains (R,
W) and W.[[NoTear]] is
true , do- If R and W have equal ranges
and
there exists an event V such that V and W have equal
ranges, V.[[NoTear]] is
true , W is not V, and execution.[[ReadsFrom]] contains (R, V), then- Return
false .
- Return
- If R and W have equal ranges
and
there exists an event V such that V and W have equal
ranges, V.[[NoTear]] is
- If R.[[NoTear]] is
- Return
true .
An event's [[NoTear]] field is
Intuitively, this requirement says when a memory range is accessed in an aligned fashion via an
29.7.4 Sequentially Consistent Atomics
For a
- For each pair (E, D) in execution.[[HappensBefore]], (E, D) is in memory-order.
-
For each pair (R, W) in execution.[[ReadsFrom]], there is no
WriteSharedMemory orReadModifyWriteSharedMemory event V inSharedDataBlockEventSet (execution) such that V.[[Order]] isseq-cst , the pairs (W, V) and (V, R) are in memory-order, and any of the following conditions are true.- execution.[[SynchronizesWith]] contains the pair (W, R), and V and R have equal ranges.
- The pairs (W, R) and (V, R) are in
execution.[[HappensBefore]], W.[[Order]] is
seq-cst , and W and V have equal ranges. - The pairs (W, R) and (W, V) are in
execution.[[HappensBefore]], R.[[Order]] is
seq-cst , and V and R have equal ranges.
Note 1 This clause additionally constrains
seq-cst events on equal ranges. -
For each
WriteSharedMemory orReadModifyWriteSharedMemory event W inSharedDataBlockEventSet (execution), if W.[[Order]] isseq-cst , then it is not the case that there is an infinite number ofReadSharedMemory orReadModifyWriteSharedMemory events inSharedDataBlockEventSet (execution) with equal range that is memory-order before W.Note 2
A
While memory-order includes all events in
29.7.5 Valid Executions
A
- The
host provides ahost-synchronizes-with Relation for execution.[[HostSynchronizesWith]]. - execution.[[HappensBefore]] is a
strict partial order . - execution has valid chosen reads.
- execution has coherent reads.
- execution has tear free reads.
- execution has sequentially consistent atomics.
All programs have at least one valid execution.
29.8 Races
For an execution execution, two events E and D in
- If E is not D, then
- If the pairs (E, D) and (D,
E) are not in execution.[[HappensBefore]], then
- If E and D are both
WriteSharedMemory orReadModifyWriteSharedMemory events and E and D do not have disjoint ranges, then- Return
true .
- Return
- If execution.[[ReadsFrom]] contains either (E, D) or
(D,
E), then
- Return
true .
- Return
- If E and D are both
- If the pairs (E, D) and (D,
E) are not in execution.[[HappensBefore]], then
- Return
false .
29.9 Data Races
For an execution execution, two events E and D in
- If E and D are in a race in
execution, then
- If E.[[Order]] is not
seq-cst or D.[[Order]] is notseq-cst , then- Return
true .
- Return
- If E and D have overlapping ranges,
then
- Return
true .
- Return
- If E.[[Order]] is not
- Return
false .
29.10 Data Race Freedom
An execution execution is data race free if there are no two events in
A program is data race free if all its executions are data race free.
The
29.11 Shared Memory Guidelines
The following are guidelines for ECMAScript programmers working with shared memory.
We recommend programs be kept data race free, i.e., make it so that it is impossible for there to be
concurrent non-atomic operations on the same memory location. Data race free programs have
interleaving
semantics where each step in the evaluation semantics of each
More generally, even if a program is not data race free it may have predictable behaviour, so long as atomic operations are not involved in any data races and the operations that race all have the same access size. The simplest way to arrange for atomics not to be involved in races is to ensure that different memory cells are used by atomic and non-atomic operations and that atomic accesses of different sizes are not used to access the same cells at the same time. Effectively, the program should treat shared memory as strongly typed as much as possible. One still cannot depend on the ordering and timing of non-atomic accesses that race, but if memory is treated as strongly typed the racing accesses will not "tear" (bits of their values will not be mixed).
The following are guidelines for ECMAScript implementers writing compiler transformations for programs using shared memory.
It is desirable to allow most program transformations that are valid in a single-
Let an agent-order slice be the subset of the
Let possible read values of a read event be the set of all values of
Any transformation of an agent-order slice that is valid in the absence of shared memory is valid in the presence of shared memory, with the following exceptions.
-
Atomics are carved in stone: Program transformations must not cause the
seq-cst events in an agent-order slice to be reordered with itsunordered operations, nor itsseq-cst operations to be reordered with each other, nor may a program transformation remove aseq-cst operation from theagent-order .(In practice, the prohibition on reorderings forces a compiler to assume that every
seq-cst operation is a synchronization and included in the finalmemory-order , which it would usually have to assume anyway in the absence of inter-agent program analysis. It also forces the compiler to assume that every call where the callee's effects on thememory-order are unknown may containseq-cst operations.) -
Reads must be stable: Any given shared memory read must only observe a single value in an execution.
(For example, if what is semantically a single read in the program is executed multiple times then the program is subsequently allowed to observe only one of the values read. A transformation known as rematerialization can violate this rule.)
-
Writes must be stable: All observable writes to shared memory must follow from program semantics in an execution.
(For example, a transformation may not introduce certain observable writes, such as by using read-modify-write operations on a larger location to write a smaller datum, writing a value to memory that the program could not have written, or writing a just-read value back to the location it was read from, if that location could have been overwritten by another
agent after the read.) -
Possible read values must be non-empty: Program transformations cannot cause the possible read values of a shared memory read to become empty.
(Counterintuitively, this rule in effect restricts transformations on writes, because writes have force in
memory model insofar as to be read by read events. For example, writes may be moved and coalesced and sometimes reordered between twoseq-cst operations, but the transformation may not remove every write that updates a location; some write must be preserved.)
Examples of transformations that remain valid are: merging multiple non-atomic reads from the same
location, reordering non-atomic reads, introducing speculative non-atomic reads, merging multiple
non-atomic writes to the same location, reordering non-atomic writes to different locations, and
hoisting
non-atomic reads out of loops even if that affects termination. Note in general that aliased
The following are guidelines for ECMAScript implementers generating machine code for shared memory accesses.
For architectures with memory models no weaker than those of ARM or Power, non-atomic stores and
loads
may be compiled to bare stores and loads on the target architecture. Atomic stores and loads may be
compiled down to instructions that guarantee sequential consistency. If no such instructions exist,
memory
barriers are to be employed, such as placing barriers on both sides of a bare store or load.
Read-modify-write operations may be compiled to read-modify-write instructions on the target
architecture,
such as LOCK-prefixed instructions on x86, load-exclusive/store-exclusive instructions on
ARM, and load-link/store-conditional instructions on Power.
Specifically, the
- Every atomic operation in the program is assumed to be necessary.
- Atomic operations are never rearranged with each other or with non-atomic operations.
- Functions are always assumed to perform atomic operations.
- Atomic operations are never implemented as read-modify-write operations on larger data, but as non-lock-free atomics if the platform does not have atomic operations of the appropriate size. (We already assume that every platform has normal memory access operations of every interesting size.)
Naive code generation uses these patterns:
- Regular loads and stores compile to single load and store instructions.
- Lock-free atomic loads and stores compile to a full (sequentially consistent) fence, a regular load or store, and a full fence.
- Lock-free atomic read-modify-write accesses compile to a full fence, an atomic read-modify-write instruction sequence, and a full fence.
- Non-lock-free atomics compile to a spinlock acquire, a full fence, a series of non-atomic load and store instructions, a full fence, and a spinlock release.
That mapping is correct so long as an atomic operation on an address range does not race with a
non-atomic write or with an atomic operation of different size. However, that is all we need: the
Local improvements to those basic patterns are also allowed, subject to the constraints of the
- There are obvious platform-dependent improvements that remove redundant fences. For example, on
x86
the fences around lock-free atomic loads and stores can always be omitted except for the fence
following
a store, and no fence is needed for lock-free read-modify-write instructions, as these all use
LOCK-prefixed instructions. On many platforms there are fences of several strengths, and weaker fences can be used in certain contexts without destroying sequential consistency. - Most modern platforms support lock-free atomics for all the data sizes required by ECMAScript atomics. Should non-lock-free atomics be needed, the fences surrounding the body of the atomic operation can usually be folded into the lock and unlock steps. The simplest solution for non-lock-free atomics is to have a single lock word per SharedArrayBuffer.
- There are also more complicated platform-dependent local improvements, requiring some code analysis. For example, two back-to-back fences often have the same effect as a single fence, so if code is generated for two atomic operations in sequence, only a single fence need separate them. On x86, even a single fence separating atomic stores can be omitted, as the fence following a store is only needed to separate the store from a subsequent load.
A Grammar Summary
A.1 Lexical Grammar
A.2 Expressions
When processing an instance of the production
the interpretation of
When processing an instance of the production
the interpretation of
In certain circumstances when processing an instance of the production
the interpretation of
A.3 Statements
A.4 Functions and Classes
When processing an instance of the production
the interpretation of
When processing an instance of the production
the interpretation of
A.5 Scripts and Modules
A.6 Number Conversions
All grammar symbols not explicitly defined by the
A.7 Time Zone Offset String Format
A.8 Regular Expressions
Each \u u u \u
B Additional ECMAScript Features for Web Browsers
The ECMAScript language syntax and semantics defined in this annex are required when the ECMAScript
This annex describes various legacy features and other characteristics of web browser ECMAScript
These features are not considered part of the core ECMAScript language. Programmers should not use or assume the existence of these features and behaviours when writing new ECMAScript code. ECMAScript implementations are discouraged from implementing these features unless the implementation is part of a web browser or is required to run the same legacy ECMAScript code that web browsers encounter.
B.1 Additional Syntax
B.1.1 HTML-like Comments
The syntax and semantics of
Syntax
Similar to a
B.1.2 Regular Expressions Patterns
The syntax of
This alternative pattern grammar and semantics only changes the syntax and semantics of BMP patterns.
The
following grammar extensions include productions parameterized with the [UnicodeMode] parameter.
However,
none of these extensions change the syntax of Unicode patterns recognized when parsing with the
[UnicodeMode] parameter present on the
Syntax
When the same left-hand sides occurs with both [+UnicodeMode] and [~UnicodeMode] guards it is to control the disambiguation priority.
B.1.2.1 Static Semantics: Early Errors
The semantics of
- It is a Syntax Error if any source text is matched by this production.
Additionally, the rules for the following productions are modified with the addition of the highlighted text:
-
It is a Syntax Error if
IsCharacterClass of the firstClassAtom istrue orIsCharacterClass of the secondClassAtom istrue and this production has a [UnicodeMode] parameter. -
It is a Syntax Error if
IsCharacterClass of the firstClassAtom isfalse ,IsCharacterClass of the secondClassAtom isfalse , and theCharacterValue of the firstClassAtom is strictly greater than theCharacterValue of the secondClassAtom .
-
It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash istrue orIsCharacterClass ofClassAtom istrue and this production has a [UnicodeMode] parameter. -
It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash isfalse ,IsCharacterClass ofClassAtom isfalse , and theCharacterValue ofClassAtomNoDash is strictly greater than theCharacterValue ofClassAtom .
B.1.2.2 Static Semantics: CountLeftCapturingParensWithin and CountLeftCapturingParensBefore
In the definitions of
B.1.2.3 Static Semantics: IsCharacterClass
The semantics of
- Return
false .
B.1.2.4 Static Semantics: CharacterValue
The semantics of
- Return the numeric value of U+005C (REVERSE SOLIDUS).
- Let ch be the code point matched by
ClassControlLetter . - Let i be the numeric value of ch.
- Return the remainder of dividing i by 32.
- Return the MV of
LegacyOctalEscapeSequence (see12.9.4.3 ).
B.1.2.5 Runtime Semantics: CompileSubpattern
The semantics of
The rule for
The rule for
The rule for
B.1.2.6 Runtime Semantics: CompileAssertion
B.1.2.7 Runtime Semantics: CompileAtom
- Let A be the
CharSet containing the single character\U+005C (REVERSE SOLIDUS). - Return
CharacterSetMatcher (rer, A,false , direction).
- Let ch be the character represented by
ExtendedPatternCharacter . - Let A be a one-element
CharSet containing the character ch. - Return
CharacterSetMatcher (rer, A,false , direction).
B.1.2.8 Runtime Semantics: CompileToCharSet
The semantics of
The following two rules replace the corresponding rules of
- Let A be
CompileToCharSet of the firstClassAtom with argument rer. - Let B be
CompileToCharSet of the secondClassAtom with argument rer. - Let C be
CompileToCharSet ofClassContents with argument rer. - Let D be
CharacterRangeOrUnion (rer, A, B). - Return the union of D and C.
- Let A be
CompileToCharSet ofClassAtomNoDash with argument rer. - Let B be
CompileToCharSet ofClassAtom with argument rer. - Let C be
CompileToCharSet ofClassContents with argument rer. - Let D be
CharacterRangeOrUnion (rer, A, B). - Return the union of D and C.
In addition, the following rules are added to
- Let cv be the
CharacterValue of thisClassEscape . - Let c be the character whose character value is cv.
- Return the
CharSet containing the single character c.
- Return the
CharSet containing the single character\U+005C (REVERSE SOLIDUS).
\c
within
a
character class where it is not followed by an acceptable control character.B.1.2.8.1 CharacterRangeOrUnion ( rer, A, B )
The abstract operation CharacterRangeOrUnion takes arguments rer (a
- If
HasEitherUnicodeFlag (rer) isfalse , then - Return
CharacterRange (A, B).
B.1.2.9 Static Semantics: ParsePattern ( patternText, u, v )
The semantics of
The abstract operation
- If v is
true and u istrue , then- Let parseResult be a
List containing one or moreSyntaxError objects.
- Let parseResult be a
- Else if v is
true , then - Else if u is
true , then - Else,
- Return parseResult.
B.2 Additional Built-in Properties
When the ECMAScript
B.2.1 Additional Properties of the Global Object
The entries in
| Intrinsic Name | Global Name | ECMAScript Language Association |
|---|---|---|
|
|
escape
|
The escape function ( |
|
|
unescape
|
The unescape function ( |
B.2.1.1 escape ( string )
This function is a property of the
When replacing a code unit of numeric value less than or equal to 0x00FF, a two-digit escape sequence
of
the form %xx is used. When replacing a code unit of numeric value strictly
greater
than 0x00FF, a four-digit escape sequence of the form %uxxxx is used.
It is the %escape% intrinsic object.
It performs the following steps when called:
- Set string to ?
ToString (string). - Let len be the length of string.
- Let R be the empty String.
- Let unescapedSet be the
string-concatenation ofthe ASCII word characters and"@*+-./" . - Let k be 0.
- Repeat, while k < len,
- Let C be the code unit at index k within string.
- If unescapedSet contains C, then
- Let S be C.
- Else,
- Let n be the numeric value of C.
- If n < 256, then
- Let hex be the String representation of n, formatted as an uppercase hexadecimal number.
- Let S be the
string-concatenation of"%" andStringPad (hex, 2,"0" ,start ).
- Else,
- Let hex be the String representation of n, formatted as an uppercase hexadecimal number.
- Let S be the
string-concatenation of"%u" andStringPad (hex, 4,"0" ,start ).
- Set R to the
string-concatenation of R and S. - Set k to k + 1.
- Return R.
The encoding is partly based on the encoding described in RFC 1738, but the entire encoding specified in this standard is described above without regard to the contents of RFC 1738. This encoding does not reflect changes to RFC 1738 made by RFC 3986.
B.2.1.2 unescape ( string )
This function is a property of the escape function is replaced with the code unit that it represents.
It is the %unescape% intrinsic object.
It performs the following steps when called:
- Set string to ?
ToString (string). - Let len be the length of string.
- Let R be the empty String.
- Let k be 0.
- Repeat, while k < len,
- Let C be the code unit at index k within string.
- If C is the code unit 0x0025 (PERCENT SIGN),
then
- Let hexDigits be the empty String.
- Let optionalAdvance be 0.
- If k + 5 < len and the
code
unit at index k + 1 within string is the code unit 0x0075 (LATIN
SMALL
LETTER U), then
- Set hexDigits to the
substring of string from k + 2 to k + 6. - Set optionalAdvance to 5.
- Set hexDigits to the
- Else if k + 3 ≤ len, then
- Set hexDigits to the
substring of string from k + 1 to k + 3. - Set optionalAdvance to 2.
- Set hexDigits to the
- Let parseResult be
ParseText (StringToCodePoints (hexDigits),HexDigits ).[~Sep] - If parseResult is a
Parse Node , then- Let n be the MV of parseResult.
- Set C to the code unit whose numeric value is n.
- Set k to k + optionalAdvance.
- Set R to the
string-concatenation of R and C. - Set k to k + 1.
- Return R.
B.2.2 Additional Properties of the String.prototype Object
B.2.2.1 String.prototype.substr ( start, length )
This method returns a
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let size be the length of S.
- Let intStart be ?
ToIntegerOrInfinity (start). - If intStart = -∞, set intStart to 0.
- Else if intStart < 0, set intStart
to
max (size + intStart, 0). - Else, set intStart to
min (intStart, size). - If length is
undefined , let intLength be size; otherwise let intLength be ?ToIntegerOrInfinity (length). - Set intLength to the result of
clamping intLength between 0 and size. - Let intEnd be
min (intStart + intLength, size). - Return the
substring of S from intStart to intEnd.
This method is intentionally generic; it does not require that its
B.2.2.2 String.prototype.anchor ( name )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"a" ,"name" , name).
B.2.2.2.1 CreateHTML ( string, tag, attribute, value )
The abstract operation CreateHTML takes arguments string (an
- Let str be ?
RequireObjectCoercible (string). - Let S be ?
ToString (str). - Let p1 be the
string-concatenation of"<" and tag. - If attribute is not the empty String, then
- Let V be ?
ToString (value). - Let escapedV be the String value that is the
same as V except that each occurrence of the code unit 0x0022 (QUOTATION MARK) in
V has been replaced with the six code unit sequence
""" . - Set p1 to the
string-concatenation of:- p1
- the code unit 0x0020 (SPACE)
- attribute
- the code unit 0x003D (EQUALS SIGN)
- the code unit 0x0022 (QUOTATION MARK)
- escapedV
- the code unit 0x0022 (QUOTATION MARK)
- Let V be ?
- Let p2 be the
string-concatenation of p1 and">" . - Let p3 be the
string-concatenation of p2 and S. - Let p4 be the
string-concatenation of p3,"</" , tag, and">" . - Return p4.
B.2.2.3 String.prototype.big ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"big" ,"" ,"" ).
B.2.2.4 String.prototype.blink ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"blink" ,"" ,"" ).
B.2.2.5 String.prototype.bold ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"b" ,"" ,"" ).
B.2.2.6 String.prototype.fixed ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"tt" ,"" ,"" ).
B.2.2.7 String.prototype.fontcolor ( color )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"font" ,"color" , color).
B.2.2.8 String.prototype.fontsize ( size )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"font" ,"size" , size).
B.2.2.9 String.prototype.italics ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"i" ,"" ,"" ).
B.2.2.10 String.prototype.link ( url )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"a" ,"href" , url).
B.2.2.11 String.prototype.small ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"small" ,"" ,"" ).
B.2.2.12 String.prototype.strike ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"strike" ,"" ,"" ).
B.2.2.13 String.prototype.sub ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"sub" ,"" ,"" ).
B.2.2.14 String.prototype.sup ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"sup" ,"" ,"" ).
B.2.2.15 String.prototype.trimLeft ( )
The property
The initial value of the
B.2.2.16 String.prototype.trimRight ( )
The property
The initial value of the
B.2.3 Additional Properties of the Date.prototype Object
B.2.3.1 Date.prototype.getYear ( )
The getFullYear method is preferred for nearly all purposes, because it avoids the
“year
2000 problem.”
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
YearFromTime (LocalTime (t)) -1900 𝔽.
B.2.3.2 Date.prototype.setYear ( year )
The setFullYear method is preferred for nearly all purposes, because it avoids the
“year
2000 problem.”
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let y be ?
ToNumber (year). - If t is
NaN , set t to+0 𝔽; otherwise, set t toLocalTime (t). - Let yyyy be
MakeFullYear (y). - Let d be
MakeDay (yyyy,MonthFromTime (t),DateFromTime (t)). - Let date be
MakeDate (d,TimeWithinDay (t)). - Let u be
TimeClip (UTC (date)). - Set dateObject.[[DateValue]] to u.
- Return u.
B.2.3.3 Date.prototype.toGMTString ( )
The toUTCString method is preferred. This method is provided principally for
compatibility with old code.
The initial value of the
B.2.4 Additional Properties of the RegExp.prototype Object
B.2.4.1 RegExp.prototype.compile ( pattern, flags )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[RegExpMatcher]]). - If pattern
is an Object and pattern has a [[RegExpMatcher]] internal slot, then- If flags is not
undefined , throw aTypeError exception. - Let P be pattern.[[OriginalSource]].
- Let F be pattern.[[OriginalFlags]].
- If flags is not
- Else,
- Let P be pattern.
- Let F be flags.
- Return ?
RegExpInitialize (O, P, F).
This method completely reinitializes the
B.3 Other Additional Features
B.3.1 Labelled Function Declarations
Prior to ECMAScript 2015, the specification of
-
It is a Syntax Error if any source text that is
strict mode code is matched by this production.
The
B.3.2 Block-Level Function Declarations Web Legacy Compatibility Semantics
Prior to ECMAScript 2015, the ECMAScript specification did not define the occurrence of a
-
A function is declared and only referenced within a single block.
-
One or more
FunctionDeclaration s whoseBindingIdentifier is the name f occur within the function code of an enclosing function g and that declaration is nested within aBlock . -
No other declaration of f that is not a
vardeclaration occurs within the function code of g. -
All occurrences of f as an
IdentifierReference are within theStatementList of theBlock containing the declaration of f.
-
One or more
-
A function is declared and possibly used within a single
Block but also referenced by an inner function definition that is not contained within that sameBlock .-
One or more
FunctionDeclaration s whoseBindingIdentifier is the name f occur within the function code of an enclosing function g and that declaration is nested within aBlock . -
No other declaration of f that is not a
vardeclaration occurs within the function code of g. -
There may be occurrences of f as an
IdentifierReference within theStatementList of theBlock containing the declaration of f. -
There is at least one occurrence of f as an
IdentifierReference within another function h that is nested within g and no other declaration of f shadows the references to f from within h. - All invocations of h occur after the declaration of f has been evaluated.
-
One or more
-
A function is declared and possibly used within a single block but also referenced within subsequent blocks.
-
One or more
FunctionDeclaration whoseBindingIdentifier is the name f occur within the function code of an enclosing function g and that declaration is nested within aBlock . -
No other declaration of f that is not a
vardeclaration occurs within the function code of g. -
There may be occurrences of f as an
IdentifierReference within theStatementList of theBlock containing the declaration of f. -
There is at least one occurrence of f as an
IdentifierReference within the function code of g that lexically follows theBlock containing the declaration of f.
-
One or more
The first use case is interoperable with the semantics of
ECMAScript 2015 interoperability for the second and third use cases requires the following extensions
to
the clause
If an ECMAScript implementation has a mechanism for reporting diagnostic warning messages, a warning
should
be produced when code contains a
B.3.2.1 Changes to FunctionDeclarationInstantiation
During
- If strict is
false , then- For each
FunctionDeclaration f that is directly contained in theStatementList of aBlock ,CaseClause , orDefaultClause , do- Let F be
StringValue of theBindingIdentifier of f. - If replacing the
FunctionDeclaration f with aVariableStatement that has F as aBindingIdentifier would not produce any Early Errors for func and parameterNames does not contain F, then- NOTE: A var binding for F is only
instantiated here if it is neither a VarDeclaredName, the name of a formal parameter,
or
another
FunctionDeclaration . - If instantiatedVarNames does not
contain
F and F is not
"arguments" , then- Perform
! varEnv.CreateMutableBinding(F,
false ). - Perform
! varEnv.InitializeBinding(F,
undefined ). - Append F to instantiatedVarNames.
- Perform
! varEnv.CreateMutableBinding(F,
- When the
FunctionDeclaration f is evaluated, perform the following steps in place of theFunctionDeclaration Evaluation algorithm provided in15.2.6 :- Let fenv be the
running execution context 's VariableEnvironment. - Let benv be the
running execution context 's LexicalEnvironment. - Let fobj be
! benv.GetBindingValue(F,
false ). - Perform
! fenv.SetMutableBinding(F, fobj,
false ). - Return
unused .
- Let fenv be the
- NOTE: A var binding for F is only
instantiated here if it is neither a VarDeclaredName, the name of a formal parameter,
or
another
- Let F be
- For each
B.3.2.2 Changes to GlobalDeclarationInstantiation
During
- Perform the following steps:
- Let strict be
IsStrict of script. - If strict is
false , then- Let declaredFunctionOrVarNames be the
list-concatenation of declaredFunctionNames and declaredVarNames. - For each
FunctionDeclaration f that is directly contained in theStatementList of aBlock ,CaseClause , orDefaultClause Contained within script, do- Let F be
StringValue of theBindingIdentifier of f. - If replacing the
FunctionDeclaration f with aVariableStatement that has F as aBindingIdentifier would not produce any Early Errors for script, then- If
env.HasLexicalDeclaration(F) is
false , then- Let fnDefinable be ? env.CanDeclareGlobalVar(F).
- If fnDefinable is
true , then- NOTE: A var binding for F
is
only instantiated here if it is neither a VarDeclaredName nor the name of
another
FunctionDeclaration . - If
declaredFunctionOrVarNames
does not contain F, then
- Perform
? env.CreateGlobalVarBinding(F,
false ). - Append F to declaredFunctionOrVarNames.
- Perform
? env.CreateGlobalVarBinding(F,
- When the
FunctionDeclaration f is evaluated, perform the following steps in place of theFunctionDeclaration Evaluation algorithm provided in15.2.6 :- Let genv be the
running execution context 's VariableEnvironment. - Let benv be the
running execution context 's LexicalEnvironment. - Let fobj be
! benv.GetBindingValue(F,
false ). - Perform ? genv.SetMutableBinding(F,
fobj,
false ). - Return
unused .
- Let genv be the
- NOTE: A var binding for F
is
only instantiated here if it is neither a VarDeclaredName nor the name of
another
- If
env.HasLexicalDeclaration(F) is
- Let F be
- Let declaredFunctionOrVarNames be the
- Let strict be
B.3.2.3 Changes to EvalDeclarationInstantiation
During
- If strict is
false , then- Let declaredFunctionOrVarNames be the
list-concatenation of declaredFunctionNames and declaredVarNames. - For each
FunctionDeclaration f that is directly contained in theStatementList of aBlock ,CaseClause , orDefaultClause Contained within body, do- Let F be
StringValue of theBindingIdentifier of f. - If replacing the
FunctionDeclaration f with aVariableStatement that has F as aBindingIdentifier would not produce any Early Errors for body, then- Let bindingExists be
false . - Let thisEnv be lexEnv.
Assert : The following loop will terminate.- Repeat, while thisEnv is not
varEnv,
- If thisEnv
is not an Object Environment Record , then- If
! thisEnv.HasBinding(F) is
true , then- Let bindingExists be
true .
- Let bindingExists be
- If
! thisEnv.HasBinding(F) is
- Set thisEnv to thisEnv.[[OuterEnv]].
- If thisEnv
- If bindingExists is
false and varEnv is aGlobal Environment Record , then- If
varEnv.HasLexicalDeclaration(F) is
false , then- Let fnDefinable be ? varEnv.CanDeclareGlobalVar(F).
- Else,
- Let fnDefinable be
false .
- Let fnDefinable be
- If
varEnv.HasLexicalDeclaration(F) is
- Else,
- Let fnDefinable be
true .
- Let fnDefinable be
- If bindingExists is
false and fnDefinable istrue , then- If declaredFunctionOrVarNames does
not
contain F, then
- If varEnv is a
Global Environment Record , then- Perform
? varEnv.CreateGlobalVarBinding(F,
true ).
- Perform
? varEnv.CreateGlobalVarBinding(F,
- Else,
- Let bindingExists be ! varEnv.HasBinding(F).
- If bindingExists is
false , then- Perform
! varEnv.CreateMutableBinding(F,
true ). - Perform
! varEnv.InitializeBinding(F,
undefined ).
- Perform
! varEnv.CreateMutableBinding(F,
- Append F to declaredFunctionOrVarNames.
- If varEnv is a
- When the
FunctionDeclaration f is evaluated, perform the following steps in place of theFunctionDeclaration Evaluation algorithm provided in15.2.6 :- Let genv be the
running execution context 's VariableEnvironment. - Let benv be the
running execution context 's LexicalEnvironment. - Let fobj be
! benv.GetBindingValue(F,
false ). - Perform ? genv.SetMutableBinding(F,
fobj,
false ). - Return
unused .
- Let genv be the
- If declaredFunctionOrVarNames does
not
contain F, then
- Let bindingExists be
- Let F be
- Let declaredFunctionOrVarNames be the
B.3.2.4 Changes to Block Static Semantics: Early Errors
The rules for the following production in
-
It is a Syntax Error if the
LexicallyDeclaredNames ofStatementList contains any duplicate entries, unless thesource text matched by this production is notstrict mode code and the duplicate entries are only bound by FunctionDeclarations. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofStatementList also occurs in theVarDeclaredNames ofStatementList .
B.3.2.5 Changes to switch Statement Static Semantics: Early
Errors
The rules for the following production in
-
It is a Syntax Error if the
LexicallyDeclaredNames ofCaseBlock contains any duplicate entries, unless thesource text matched by this production is notstrict mode code and the duplicate entries are only bound by FunctionDeclarations. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofCaseBlock also occurs in theVarDeclaredNames ofCaseBlock .
B.3.2.6 Changes to BlockDeclarationInstantiation
During
- If ! env.HasBinding(dn) is
false , then- Perform
! env.CreateMutableBinding(dn,
false ).
- Perform
! env.CreateMutableBinding(dn,
During
- Perform the following steps:
- If the binding for fn in env is an
uninitialized binding, then
- Perform ! env.InitializeBinding(fn, fo).
- Else,
Assert : d is aFunctionDeclaration .- Perform
! env.SetMutableBinding(fn, fo,
false ).
- If the binding for fn in env is an
uninitialized binding, then
B.3.3 FunctionDeclarations in IfStatement Statement Clauses
The following augments the
This production only applies when parsing
B.3.4 VariableStatements in Catch Blocks
The content of subclause
-
It is a Syntax Error if
BoundNames ofCatchParameter contains any duplicate elements. -
It is a Syntax Error if any element of the
BoundNames ofCatchParameter also occurs in theLexicallyDeclaredNames ofBlock . -
It is a Syntax Error if any element of the
BoundNames ofCatchParameter also occurs in theVarDeclaredNames ofBlock unlessCatchParameter isCatchParameter : BindingIdentifier
The var declarations that bind a name that is also bound by the var declarations will assign to the corresponding catch parameter rather than the
var binding.
This modified behaviour also applies to var and function declarations
introduced
by
Step
- If thisEnv is not the
Environment Record for aCatch clause, throw aSyntaxError exception.
Step
- If thisEnv is not the
Environment Record for aCatch clause, let bindingExists betrue .
B.3.5 Initializers in ForIn Statement Heads
The following augments the
This production only applies when parsing
The
- Return
ContainsDuplicateLabels ofStatement with argument labelSet.
The
- Return
ContainsUndefinedBreakTarget ofStatement with argument labelSet.
The
- Return
ContainsUndefinedContinueTarget ofStatement with arguments iterationSet and « ».
The
- Return
false .
The
- Let names1 be the
BoundNames ofBindingIdentifier . - Let names2 be the
VarDeclaredNames ofStatement . - Return the
list-concatenation of names1 and names2.
The
- Let declarations1 be «
BindingIdentifier ». - Let declarations2 be the
VarScopedDeclarations ofStatement . - Return the
list-concatenation of declarations1 and declarations2.
The
- Let bindingId be
StringValue ofBindingIdentifier . - Let lhs be ?
ResolveBinding (bindingId). - If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Let value be ?
NamedEvaluation ofInitializer with argument bindingId.
- Let value be ?
- Else,
- Let rhs be ?
Evaluation ofInitializer . - Let value be ?
GetValue (rhs).
- Let rhs be ?
- Perform ?
PutValue (lhs, value). - Let keyResult be ?
ForIn/OfHeadEvaluation (« »,Expression ,enumerate ). - Return ?
ForIn/OfBodyEvaluation (BindingIdentifier ,Statement , keyResult,enumerate ,var-binding , labelSet).
B.3.6 The [[IsHTMLDDA]] Internal Slot
An [[IsHTMLDDA]] internal slot may exist on typeof
operator
Objects with an [[IsHTMLDDA]] internal slot are never created by this
specification. However, the document.all
object in web browsers is a document.all.
B.3.6.1 Changes to ToBoolean
The following step replaces step
- If argument
is an Object and argument has an [[IsHTMLDDA]] internal slot, returnfalse .
B.3.6.2 Changes to IsLooselyEqual
The following steps replace step
- Perform the following steps:
- If x
is an Object , x has an [[IsHTMLDDA]] internal slot, and y is eitherundefined ornull , returntrue . - If x is either
undefined ornull , yis an Object , and y has an [[IsHTMLDDA]] internal slot, returntrue .
- If x
B.3.6.3 Changes to the typeof Operator
The following step replaces step typeof
- If val has an [[IsHTMLDDA]]
internal slot, return
"undefined" .
B.3.7 Non-default behaviour in HostMakeJobCallback
The
B.3.8 Non-default behaviour in HostEnsureCanAddPrivateElement
The
C The Strict Mode of ECMAScript
The strict mode restriction and exceptions
-
implements,interface,let,package,private,protected,public,static, andyieldarereserved words withinstrict mode code . (12.7.2 ). -
A conforming implementation, when processing
strict mode code , must disallow instances of the productionsNumericLiteral :: LegacyOctalIntegerLiteral DecimalIntegerLiteral :: NonOctalDecimalIntegerLiteral -
A conforming implementation, when processing
strict mode code , must disallow instances of the productionsEscapeSequence :: LegacyOctalEscapeSequence EscapeSequence :: NonOctalDecimalEscapeSequence -
Assignment to an undeclared identifier or otherwise unresolvable reference does not create a property in
the
global object . When a simple assignment occurs withinstrict mode code , itsLeftHandSideExpression must not evaluate to an unresolvable Reference. If it does aReferenceError exception is thrown (6.2.5.6 ). TheLeftHandSideExpression also may not be a reference to adata property with the attribute value { [[Writable]]:false }, to anaccessor property with the attribute value { [[Set]]:undefined }, nor to a non-existent property of an object whose [[Extensible]] internal slot isfalse . In these cases aTypeErrorexception is thrown (13.15 ). -
An
IdentifierReference with theStringValue "eval" or"arguments" may not appear as theLeftHandSideExpression of an Assignment operator (13.15 ) or of anUpdateExpression (13.4 ) or as theUnaryExpression operated upon by a Prefix Increment (13.4.4 ) or a Prefix Decrement (13.4.5 ) operator. -
Arguments objects for
strict functions define a non-configurableaccessor property "callee" which throws aTypeError exception on access (10.4.4.6 ). -
Arguments objects for
strict functions do not dynamically share theirarray-indexed property values with the corresponding formal parameter bindings of their functions. (10.4.4 ). -
For
strict functions , if an arguments object is created the binding of the local identifierargumentsto the arguments object is immutable and hence may not be the target of an assignment expression. (10.2.11 ). -
It is a
SyntaxError if theStringValue of aBindingIdentifier is either"eval" or"arguments" withinstrict mode code (13.1.1 ). -
Strict mode eval code cannot instantiate variables or functions in the variable environment of the caller
to
eval. Instead, a new variable environment is created and that environment is used for declaration binding
instantiation for the eval code (
19.2.1 ). -
If
this is evaluated withinstrict mode code , then thethis value is not coerced to an object. Athis value of eitherundefined ornull is not converted to theglobal object and primitive values are not converted to wrapper objects. Thethis value passed via a function call (including calls made usingFunction.prototype.applyandFunction.prototype.call) do not coerce the passedthis value to an object (10.2.1.2 ,20.2.3.1 ,20.2.3.3 ). -
When a
deleteoperator occurs withinstrict mode code , aSyntaxError is thrown if itsUnaryExpression is a direct reference to a variable, function argument, or function name (13.5.1.1 ). -
When a
deleteoperator occurs withinstrict mode code , aTypeError is thrown if the property to be deleted has the attribute { [[Configurable]]:false } or otherwise cannot be deleted (13.5.1.2 ). -
Strict mode code may not include aWithStatement . The occurrence of aWithStatement in such a context is aSyntaxError (14.11.1 ). -
It is a
SyntaxError if aCatchParameter occurs withinstrict mode code andBoundNames ofCatchParameter contains eitherevalorarguments(14.15.1 ). -
It is a
SyntaxError if the sameBindingIdentifier appears more than once in theFormalParameters of astrict function . An attempt to create such a function using a Function, Generator, or AsyncFunctionconstructor is aSyntaxError (15.2.1 ,20.2.1.1.1 ). -
An implementation may not extend, beyond that defined in this specification, the meanings within
strict functions of properties named"caller" or"arguments" of function instances.
D Host Layering Points
See
D.1 Host Hooks
D.2 Host-defined Fields
[[HostDefined]] on
[[HostDefined]] on
[[HostDefined]] on
[[HostDefined]] on
[[HostSynchronizesWith]] on Candidate Executions: See
[[IsHTMLDDA]]: See
D.3 Host-defined Objects
The
D.4 Running Jobs
Preparation steps before, and cleanup steps after, invocation of
D.5 Internal Methods of Exotic Objects
Any of the essential internal methods in
D.6 Built-in Objects and Methods
Any built-in objects and methods not defined within this specification, except as restricted in
E Corrections and Clarifications in ECMAScript 2015 with Possible Compatibility Impact
Date.prototype.toString when the
/.
String.prototype.match and
String.prototype.replace
was incorrect for cases where the pattern argument was a RegExp value whose global flag is set.
The
previous specifications stated that for each attempt to match the pattern, if lastIndex did not
change, it should be incremented by 1. The correct behaviour is that lastIndex should be
incremented by 1 only if the pattern matched the empty String.
Array.prototype.sort. ECMAScript 2015 specifies that such as value is treated as if
F Additions and Changes That Introduce Incompatibilities with Prior Editions
Space_Separator (Zs) category
and
thus treated as whitespace in ECMAScript 2015, to be moved to the Format (Cf)
category
(as of Unicode 6.3.0). This causes whitespace-sensitive methods to behave differently. For example,
"\u180E".trim().length was 0 in previous editions, but 1 in
ECMAScript
2016 and later. Additionally, ECMAScript 2017 mandated always using the latest version of the Unicode
Standard.
let followed by the token [ is the start of a
( token of a for statement is immediately followed by the token sequence let [
then the let is treated as the start of a
let [ then the
let is treated as the start of a
in
var
declaration for the same
eval whose eval code includes a var or FunctionDeclaration
declaration
that binds the same
Object.freeze is not an object it is treated as if it was a non-extensible
Object.getOwnPropertyDescriptor is not an object an attempt
is
made to coerce the argument using
Object.getOwnPropertyNames is not an object an attempt is made to
coerce
the argument using
Object.getPrototypeOf is not an object an attempt is made to coerce the
argument
using
Object.isExtensible is not an object it is treated as if it was a
non-extensible
Object.isFrozen is not an object it is treated as if it was a non-extensible
Object.isSealed is not an object it is treated as if it was a non-extensible
Object.keys is not an object an attempt is made to coerce the argument using
Object.preventExtensions is not an object it is treated as if it was a
non-extensible
Object.seal is not an object it is treated as if it was a non-extensible
String.prototype.localeCompare function must treat Strings that are
canonically equivalent according to the Unicode Standard as being identical. In previous editions
implementations were permitted to ignore canonical equivalence and could instead use a bit-wise comparison.
String.prototype.trim method is defined to recognize white space code points that may exist
outside of the Unicode BMP. However, as of Unicode 7 no such code points are defined. In previous editions
such
code points would not have been recognized as white space.
Atomics.wake has been renamed to Atomics.notify to prevent confusion with
Atomics.wait.
await was reduced,
which could create an observable difference in resolution order between a then() call and an
await expression.
G Colophon
This specification is authored on GitHub in a plaintext source format called Ecmarkup. Ecmarkup is an HTML and Markdown dialect that provides a framework and toolset for authoring ECMAScript specifications in plaintext and processing the specification into a full-featured HTML rendering that follows the editorial conventions for this document. Ecmarkup builds on and integrates a number of other formats and technologies including Grammarkdown for defining syntax and Ecmarkdown for authoring algorithm steps. PDF renderings of this specification are produced by printing the HTML rendering to a PDF.
Prior editions of this specification were authored using Word—the Ecmarkup source text that formed the basis of this edition was produced by converting the ECMAScript 2015 Word document to Ecmarkup using an automated conversion tool.
H Bibliography
-
IEEE 754-2019: IEEE Standard for Floating-Point Arithmetic. Institute of
Electrical and Electronic Engineers, New York (2019)
Note There are no normative changes between IEEE 754-2008 and IEEE 754-2019 that affect the ECMA-262 specification.
- The Unicode Standard, available at <https://unicode.org/versions/latest>
- Unicode Technical Note #5: Canonical Equivalence in Applications, available at <https://unicode.org/notes/tn5/>
- Unicode Technical Standard #10: Unicode Collation Algorithm, available at <https://unicode.org/reports/tr10/>
- Unicode Standard Annex #15, Unicode Normalization Forms, available at <https://unicode.org/reports/tr15/>
- Unicode Standard Annex #18: Unicode Regular Expressions, available at <https://unicode.org/reports/tr18/>
-
Unicode Standard Annex #24: Unicode
ScriptProperty, available at <https://unicode.org/reports/tr24/> - Unicode Standard Annex #31, Unicode Identifiers and Pattern Syntax, available at <https://unicode.org/reports/tr31/>
- Unicode Standard Annex #44: Unicode Character Database, available at <https://unicode.org/reports/tr44/>
- Unicode Technical Standard #51: Unicode Emoji, available at <https://unicode.org/reports/tr51/>
- IANA Time Zone Database, available at <https://www.iana.org/time-zones>
- ISO 8601:2004(E) Data elements and interchange formats — Information interchange — Representation of dates and times
- RFC 1738 “Uniform Resource Locators (URL)”, available at <https://tools.ietf.org/html/rfc1738>
- RFC 2396 “Uniform Resource Identifiers (URI): Generic Syntax”, available at <https://tools.ietf.org/html/rfc2396>
- RFC 3629 “UTF-8, a transformation format of ISO 10646”, available at <https://tools.ietf.org/html/rfc3629>
- RFC 7231 “Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content”, available at <https://tools.ietf.org/html/rfc7231>
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